Examining Students’ Conceptions
Running Head: STUDENTS’ CONCEPTIONS OF GENETICS
Examining Students’ Conceptions of Molecular Genetics
in an Introductory Biology Course for Non-Science Majors:
A Self Study
Patricia Meis Friedrichsen and Bethany Stone
University of Missouri - Columbia
Patrick Brown
Mexico Public Schools, MO
Paper presented at the National Association for Research in Science Teaching
International Conference, Vancouver, WA, April 1-4, 2004.
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Abstract
In this self-study, Author B examined her teaching practice in an introductory biology course
with a large student enrollment. The study focuses on three target concepts in molecular
genetics: the physical relationship between genes, DNA and chromosomes; gene function and
the role of proteins; and that each cell has the complete genome for the organism and uses gene
expression for specialization. Twelve students were randomly selected to participate in pre- and
post-instructional interviews. After eliciting students’ prior understanding of the target concepts,
Author B designed conceptual change-based instruction. To examine the effectiveness of her
instruction, she compared students’ pre- and post-instructional understandings of the target
concepts. Initially, students lacked understanding of the physical relationship between genes,
DNA and chromosomes. After instruction, the majority of students were able to accurately
describe the relationship between these structures. Prior to instruction, students equated genes
with traits and described the role of proteins from a dietary perspective. After instruction, many
students expanded their definition of genes to include coding for proteins. However, most of the
students were unable to apply this idea to explain how a specific protein, hemoglobin, would be
made. In addition, few students could describe specific roles of proteins within the cell. Prior to
instruction, 9 of the 12 students held the alternative conception that cells have only the genes
they need. Once students were taught about gene expression, 10 students adopted an accurate
scientific conception.
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Stem cells, cloning, and genetically modified foods are frequent topics in today’s news.
How much does the general public understand about these complex issues? Scientific literacy is
essential if citizens are to make informed decisions regarding new scientific advances (American
Association for the Advancement of Science [AAAS], 1989, 1993). Scientific literacy includes a
conceptual understanding of genetics on a molecular level. The National Science Education
Standards recommend that the concept of genes be introduced in grades 5-8. In grades 9-12, the
Standards concentrate on the molecular basis of heredity, including the structure and function of
DNA, the transmission of genetic material, as well as genetic variation and mutations (National
Research Council [NRC], 1996). At the postsecondary level, the Information and Education
Committee of the American Society of Human Genetics (ASHG) formulated a set of content
recommendations for introductory biology courses for non-science majors (Hott et al., 2002).
The committee recommended that the following topics be included in introductory biology
courses: the nature of genetic material, transmission, gene expression, gene regulation, evolution,
and genetics and society.
However, learning genetics remains problematic for many students. A survey of firstyear university students in an introductory biology course revealed that students perceived
genetics to be a difficult topic to understand (Bahar, Johnstone & Hansell, 1999). Researchers
propose that learning difficulties are inherent in genetics because students are required to
integrate information across multiple organizational levels (Bahar et al., 1999; Duncan & Reiser,
2003; Fisher, Wandersee, & Moody, 2000; Horowitz, P., 1996; Kapteijn, 1990; Marbach-Ad, G.,
& Stavy, R., 2000). Consequently, students hold many alternative conceptions in the area of
genetics (Kindfield, 1991, Stewart & Hafner, 1994; Wood-Robinson, 1994). Unfortunately,
most biology faculty who teach undergraduate students are unaware of students’ alternative
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conceptions (Fisher et al., 2000). Furthermore, university faculty receive little formal training in
conceptual change-based teaching strategies, assessment of student learning, or evaluation of
teaching effectiveness (NRC, 2003), and as a consequence, are unprepared to help students with
these learning difficulties.
Duit and Treagust (2003) call for studies that narrow the gap between conceptual change
theory and classroom practice. This study is significant because it is a case study of a university
instructor engaged in a self-study of her teaching of molecular genetics (Hamilton, 1998). The
context of the study is one that is prevalent on university campuses, an introductory biology
course for non-science majors with a large student enrollment. The primary purpose of this selfstudy was to enhance self-knowledge to improve teaching practice (Barnes, 1998). Using
information about her students’ prior knowledge, Author B designed instruction to support
conceptual understanding of target genetic concepts. A second purpose of this self-study is to
contribute to the literature on teaching and learning molecular genetics in university-level
introductory biology courses for non-science majors.
Theoretical Framework
Conceptual Change
Conceptual change learning theory guided this study (Posner, Strike, Hewson & Gertzog,
1982; Hewson, 1981; Hewson, Beeth & Thorley, 1998). Hewson et al. (1998) state:
The central concepts of the [conceptual change] model are status and conceptual ecology.
The status that an idea has for the person holding it is an indication of the degree to which
he or she knows and accepts it: status is determined by its intelligibility, plausibility and
fruitfulness to that person. The idea of a conceptual ecology deals with all the knowledge
that a person holds, recognizes that it consists of different kinds, focuses attention on the
interactions within this knowledge base, and identifies the role that these interactions play
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in defining niches that support some ideas (raise their status) and discourage others
(reduce their status.) Learning something, then, means that the learner has raised its
status within the context of his or her conceptual ecology. (pp. 199-200)
The conceptual change model identifies four conditions that need to be met before a conception
can be accommodated into a person’s conceptual ecology: (a) there must be dissatisfaction with
existing conceptions; (b) a new conception must be intelligible; (c) a new conception must
appear initially plausible; and (d) a new conception should suggest the possibility of a fruitful
research program (Posner et al., 1982, p. 214). Hewson and Hewson (1988) offer the following
simplified definitions of the conditions above, “Learners use their existing knowledge to
determine if a new conception is intelligible (knowing what it means), plausible (believing it to
be true), and fruitful (finding it useful)” (p. 605).
Wandersee, Minzes and Novak, 1994, summarized the research on alternative
conceptions in the following way: (a) Students bring a diverse set of alternative conceptions to
formal classroom instruction; (b) alterative conceptions are resistant to conventional teaching
strategies; and (c) “learners’ prior knowledge interacts with knowledge presented in formal
instruction, resulting in a diverse set of unintended learning outcomes” (p. 190). However,
“instructional approaches that facilitate conceptual change can be effective classroom tools” (p.
191). In the next section, we give a brief overview of guidelines for teaching for conceptual
change.
Conceptual Change-based Instructional Strategies
Hewson et al. (1998) gave the following guidelines for teaching for conceptual change: a)
make students’ and teachers’ ideas an explicit part of classroom discourse; b) use metacognitive
strategies to help students think about their learning; c) discuss the status of students’ ideas; and
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d) include justification as part of the discussion of the status of ideas. These recommendations
are re-iterated in Science Teaching Reconsidered (NRC, 1997). In this report, the following
teaching recommendations are made for undergraduate science instruction: “identify students’
misconceptions; provide a forum for students to confront their misconceptions; and help students
reconstruct and internalize their knowledge, based on scientific models” (p. 29). To help
students reconstruct scientifically-based explanations, the following strategies are suggested:
• Anticipate the most common misconceptions about the material and be alert
for others.
• Encourage students to test their conceptual frameworks in discussion with other
students and by thinking about this evidence and possible tests.
• Think about how to address common misconceptions with demonstrations and lab
work.
• Revisit common misconceptions as often as you can.
• Assess and reassess the validity of student concepts (pp. 30-31).
Context of the Study
The Instructor
Author B is a post-doctorate fellow researching phototropism genes in Arabidopsis. As a
doctoral graduate student, Author B was concerned about her lack of coursework in education.
In the last year of her graduate program, Author B enrolled in a science education course for
college science instructors. In this course, Author B realized that students were not empty
vessels to be filled with knowledge, but instead came to class with their own ideas about
biological concepts. As an assignment in the college science teaching course, Author B
interviewed several students about their understandings of molecular genetics. During the
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interviews, Author B realized that students either lacked any understanding of genetic concepts
or held alternative conceptions.
During her post-doctorate fellowship, Author B began teaching a section of an
introductory biology course for non-science majors. Drawing on the college science teaching
course, Author B wanted to elicit students’ prior understandings of biology concepts before
designing instruction. She wanted to know if her students held the same alternative conceptions
that she had uncovered in the interview assignment. Author B also wanted to critically examine
her teaching practice to better understand if her instruction was supporting students’ conceptual
understanding of molecular genetics. Author A, a faculty member with a joint appointment in
biology and science education, taught a section of the same introductory course. Working within
the same problem context (a biology course for non-science majors), Author B served as critical
friend and co-researcher in the self-study. This collaboration was an essential aspect of the selfstudy (Loughran & Northfield, 1998).
The Course
During the fifteen-week semester, the class met three days a week for one-hour lecture
sessions. The classroom was a large auditorium with a seating capacity of 500. In the fall
semester of 2003, Author B’s student enrollment was 389 students, which included 185
freshmen, 164 sophomores, 31 juniors and 9 seniors. A single instructor, without the aid of
teaching assistants, taught each section of the course. Students had the option of enrolling in a
separate, one-credit laboratory course. From a review of the laboratory course syllabus and an
interview with a laboratory teaching assistant, we determined the target genetics concepts of the
study were not being taught in the laboratory course. Based on this information, we concluded
that the optional laboratory course did not have an effect on the findings of this study.
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Additional Background Information
The planning stage of the inquiry began in the fall semester of 2002. A pilot study was
conducted in the spring semester of 2003, when both authors were teaching sections of the
course. The purpose of the pilot study was to refine the data collection tools, both the student
questionnaire and the interview protocol. This paper focuses on the study conducted in Author
B’s section of the course in the fall semester of 2003. To allow the interview participants to
remain anonymous, Author A conducted the pre- and post-instructional interviews for the study.
Author B designed the instruction for her section of the course, seeking feedback from Author A.
All three authors engaged in analyzing the student data from the pre- and post-instructional
questionnaires and interviews.
Research Questions
In this study, we focused on the following three target concepts in the molecular genetics
unit: Concept 1: the physical relationship between genes, DNA and chromosomes; Concept 2:
gene function and role of proteins; and Concept 3: within an individual, each cell contains the
complete genome but not all genes are expressed. The research questions were: (a) What were
the students’ initial conceptions of the target concepts? (b) Based on information about the
students’ initial conceptions, how did the instructor design instruction to promote conceptual
understanding? And (c) What were the students’ post-instructional conceptions of the target
concepts?
Methods
Data Collection
During the first week of the course, 304 students responded to the invitation to participate
in the study. Students chose to participate at either Level 1, which granted access to their written
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work in the course, or Level 2, in which the students also agreed to participate in two 45-minute
interviews. Students received extra credit for participating in both interviews. A total of 358
students agreed to participate at Level 1 and, of those students, 304 also agreed to participate at
Level 2. From this group of students, 14 students were randomly selected to participate in two
45-minute interviews. Due to the large class enrollment, it was not feasible to obtain students’
daily attendance records. However, based on the grades of 15 small group assignments,
completed in class, we had an indication of each participant’s class attendance. At the end of the
course, two of the 14 students had missed more than three small group assignments, and were
excluded from the data set. This paper reports the data from the 12 remaining participants, whose
self-reports confirm that they missed less than three class sessions during the unit on molecular
genetics.
Pre- and post-instructional questionnaire.
All students in the course completed a pre- and post-instructional questionnaire
(Appendix A). The questionnaire consisted of 17 items, and included both free response and
fixed response items. For each of the items, students were asked to construct an explanation for
their response. The questionnaire was initially used with students in the fall semester of 2002. A
revised questionnaire was used in a pilot study in the spring semester of 2003. As part of the
pilot study, 20 students were interviewed to confirm the validity of the questions and the
students’ responses. In addition, three geneticists confirmed the validity of the questions and
gave input on revisions. Based on the interview data and feedback from the geneticists, the
questionnaire underwent additional revisions before being used in this study. Students completed
the pre-instructional questionnaire during the third week of the course. To encourage thoughtful
responses, the students were given adequate class time and earned points for the completion of
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the questionnaire items. After the molecular genetics unit, students completed the same
questionnaire as part of the unit exam.
Pre- and post-instructional interviews.
Semi-structured interviews were conducted to verify the written responses on the
questionnaire. The interviews, conducted 3-4 weeks after the molecular genetics unit test, were
audio-taped and transcribed. The interview protocol consisted of asking the participant to read
his/her written response on the pre-instructional questionnaire and then comment on their
response. When necessary, additional probing questions were asked to elicit the participant’s
understanding. In the post-instructional interview, the same participants were asked to reflect on
their original responses and to explain their current understanding of the target concepts.
In the post-instructional interview, an additional interview question was asked. After
discussing the questionnaire, students were shown a diagram from their textbook illustrating the
process used to clone Dolly, the sheep (see Krogh, 2002, p. 299). The diagram showed a
mammary cell (from sheep 1) fused to a de-nucleated donor egg (from sheep 2). The fused cell
developed into an embryo and was implanted into the uterus of a third sheep. The interviewer
reminded the student that the mammary cell was a specialized cell, not an egg. The student was
then asked to explain the source of the DNA needed to develop Dolly.
Instructional artifacts.
Author B designed her own instruction for the course, creating PowerPoint presentations.
The PowerPoint presentations served as a primary data source. Other classroom artifacts
included small group assignments, homework assignments, and Author B’s reflective notes on
instruction.
Data Analysis
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The three authors analyzed the students’ pre- and post-instructional questionnaires and
interview transcripts. Two authors read each questionnaire and interview transcript
independently. Each author created a pre-instruction and post-instruction summary of each of
the 12 participant’s understandings of the target concepts. For each participant, the summaries
were compared, and in cases of discrepancies, the data was re-examined. The group data was
then compiled. A similar procedure was used to analyze the instructional artifacts. Author A and
Author B independently analyzed the artifacts, writing summaries for each of the target concepts.
The summaries were compared and discrepancies were resolved through re-examination of the
data and further discussion between Author A and Author B.
Findings
The findings are presented in two sections, with the first section focusing on students’
understandings of the three target genetic concepts. For each target concept, students’ preinstructional and post-instructional responses are shown. The second section focuses on the
genetics instruction, specifically the instructional strategies that were used based on information
from the initial student interviews.
Students’ Understandings of Target Concepts
Target concept 1: physical relationship between DNA, genes and chromosomes.
The first target concept focused on the physical relationships between DNA, genes and
chromosomes (see Tables 1 and 2). During the pre-instructional interviews, students were asked
to draw pictures of each of these structures. When asked to draw a DNA molecule, 8 students
drew a simple ladder structure, but were unable to identify any components of the structure. One
student indicated an alternative conception by drawing a chain of chromosomes (see Figure 1).
The remaining 3 students were not able to draw any structure for DNA. When asked to draw
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chromosomes, 1 student drew an “X” structure but was unable to explain the drawing. Four
students indicated that all chromosomes are either “X” or “Y” chromosomes. Two students drew
thread-like structures but could not explain their drawings, while 2 students were not able to
draw any chromosome structure. When asked to draw genes, 10 students were unable to draw
any structure. One student drew a particle-like structure but could not explain the drawing, nor
connect it to the drawings of DNA or chromosomes. Only one student physically located a gene
in relationship to DNA and chromosomes. However, this student incorrectly drew a DNA
molecule with chromosomes making up the rungs of a ladder. The student pointed to the
centromere of each chromosome and indicated that was the location of the gene (see Figure 2).
One student was confident that genes “are not physical entities,” and insisted that a “gene is a
trait.”
Students were asked to explain the physical relationship between DNA, chromosomes
and genes. Eleven students were unable to describe any physical relationship between genes and
DNA, while one student indicated that a gene was a single rung on the DNA ladder. When asked
to describe the physical relationship between genes and chromosomes, 11 students were unable
to describe any connection. One student, as describe above, indicated that a gene was located at
the centromere of a chromosome, and the chromosome made up the rung of a DNA ladder.
When asked to describe the relationship between DNA and chromosomes, none of the students
could accurately describe the relationship. Three students indicated that each rung of the DNA
ladder was a chromosome, while the remaining 9 students could not explain any relationship.
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_____________________________________________________________________________
Insert Tables 1 and 2
_____________________________________________________________________________
In the post-instructional interviews, students were again asked to draw a DNA molecule,
a chromosome and a gene, and to explain the relationship between these structures. In the postinstructional interviews, 11 students drew the structure of DNA as a double helix, with 5 of the
11 students giving more detailed descriptions that included nitrogenous bases making up the
rungs. When asked to explain the relationship between DNA and chromosomes, 10 students
correctly described the relationship. Of these 10 students, 7 students gave detailed descriptions of
a DNA molecule wrapping around histones to form a chromosome, while the remaining 3
students gave more general explanations of chromosomes consisting of DNA. The 3 students
who initially described chromosomes as structures inside a DNA molecule changed their
explanations to chromosomes being made up of DNA. The remaining 2 students were unable to
describe the make-up of chromosomes.
Of the 12 students, 8 students were able to describe a physical relationship between genes
and DNA, describing a gene as a section of DNA or more broadly that DNA is made up of
genes. The student who had previously described a gene as a centromere of a chromosome
correctly described a gene as a section of a DNA molecule. However, in the post-instructional
interview, 2 students adopted the alternative conception of chromosomes as rungs of a DNA
ladder, while 1 student still was not able to explain any relationship between genes and DNA.
In reflecting on his understanding of the relationship between DNA, chromosomes and
genes, one student discussed the following issue of scale:
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DC: I’m positive that a chromosome is a molecule of DNA because I know I was taught
that and I know I’ve seen it in my notes and I know I’ve studied that, but with everything
I’ve ever seen in class, and not just class . . . but in books, DNA is always blown up and
it’s large so you can see the structure. And everyone always focuses on the structure, I
know it’s a double-helix, but when it comes time to draw both of them [DNA molecule
and chromosomes], it’s just…we always draw a chromosome so small.
I: Without saying we’re changing scale?
DC: Right. I mean, I guess it should be obvious if you’re thinking about it. But a lot of
people aren’t thinking about it, I guess. They’re just sitting there and … yeah, I mean if
you see something big, I guess your assumption is that it’s big. . . if I’m not really
involved or really focusing, I’m just going to be like, well, they showed a huge picture of
DNA and now they’re showing how there’s 46 little Xs in a cell and…I don’t know. If
you think extremely logically just like, well that’s big [pointing to DNA molecule], that’s
small [pointing to chromosomes], maybe those small things make up the big things. If
you’re not really paying attention and really focusing. Some people aren’t in a lecture
(DC, 2nd interview).
The student quoted above accurately described the physical relationship between DNA and
chromosomes; however, his reflection indicated that students might be confused by DNA and
chromosome illustrations when changes in scale are not made explicit.
Target concept 2: gene function and role of proteins.
When students were asked to explain what genes do, they described genes as a source of
traits (n = 10) or as a way of store information (n = 2). None of the students described genes as
coding for proteins (see Table 3). Toward the end of the interview, students were prompted to
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describe the relationship between genes and proteins. Only 1 student stated that she thought
genes coded for proteins, 1 student stated that proteins gave fuel to genes, and 10 students were
uncertain of the relationship between genes and proteins. In the pre-instructional interviews, the
excerpt below illustrates a typical student response:
I:
Question number 13 asks to explain the relationship between genes and proteins.
Please read what you wrote on the pretest.
MH: A protein is a part of gene [reading pre-test]. It might be…is it the other way
around? Is a gene a part of a protein? Explain the relationship between a gene and
a protein [re-reading the question] …I’m just not sure. I’m not sure at all. I must
have just written that because that must have been the only thing I could think of
(1st interview, p. 7).
In a follow-up question, students were asked to explain how the protein, hemoglobin, was
produced in their bodies. None of the 12 students could offer any explanation for how
hemoglobin was made.
Insert Table 3
_____________________________________________________________________________
_
After the genetics unit, 3 of the 7 students who initially defined a gene as a source of
traits changed their explanations to that of genes coding for proteins. In the post-instructional
interviews, a total of 8 students defined genes as coding for proteins (Table 1). Later in the
interview, students were prompted again to explain the relationship between genes and proteins.
Of the 12 students, 8 students explained that genes code for proteins, while 4 students were
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unable to accurately describe the relationship between genes and proteins. Students were again
asked how their bodies made the protein, hemoglobin. (Hemoglobin had not been discussed in
the class lectures.) Of the 8 students who stated that genes code for proteins, only 3 of these
students could apply this information to explain how hemoglobin would be made. In the
interview excerpt below, the student used the concept of genes to describe how hemoglobin
would be made:
CW: It’s just a certain gene codes for a building of the hemoglobin and then it goes
from there…I want to say…I’m trying to think of the process it goes through, like,
when it…a codon binds to an anitcodon and then an amino acid…see, I can’t…
I:
And you don’t have to give me the specific terms. You can just give me the
general process.
CW: See, I think I know the terms there, and I can’t. Because I know the process. Like
the codon finds the anticodon and those link up then I think it’s amino acid comes
in and binds to that and that builds this protein and then those proteins are
responsible for making the hemoglobin and that’s probably about the best answer I
can give (CW, 2nd interview, p. 10).
The student above gave the most detailed response to the hemoglobin question. The next student
also used genes in her explanation of how hemoglobin was produced in the body.
I:
Red blood cells have a protein called hemoglobin. How does your body make
this protein? On the pre-test, you wrote, “Cells take in oxygen and this gives
them the ability to make proteins.” What do you think about your answer now?
KH:
Well, I don’t think my answer is right. I think hemoglobin comes from a gene
that is turned on and says to your red blood cells to make hemoglobin. And
then…yeah.
Examining Students’ Conceptions
I:
OK. And does that make sense?
KH:
Kind of.
I:
What question do you have? You seem a little hesitant on this one.
KH:
I just don’t remember ever learning about this and…I don’t know. I just don’t
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know if my answer’s right. It makes sense to me now, but it could be wrong
because most of my answers make sense to me at the time (KH, 2nd interview, p.
8).
In this except, the student’s conception of genes being responsible for coding for proteins
appears to be fruitful; however, the conception doesn’t appear to have a high status for the
student. Of the 8 students who described genes as coding for proteins, 5 of these 8 students could
not use the concept to explain how hemoglobin, would be made. The excerpt below is typical of
the responses of these 5 students:
I:
How do cells make more hemoglobin?
KN:
I had no idea [referring to her pre-test answer]. And I still have no idea. Yeah.
I’m trying to venture a guess. . . I guess that there would be something in your
body that would kind of alert the proteins that it needed more hemoglobin to bond
with oxygen to make red blood cells.
I:
And so how would the body make more hemoglobin?
KN:
No idea (KN, 2nd interview, p.7).
Earlier in the interview, this student had explained that genes code for proteins. However, the
student does not use this idea to explain how a specific protein, hemoglobin, would be produced
in the body.
Students need to understand the relationship between genes and proteins, but they must
also develop an understanding of what proteins do on a cellular level. Ideally, students should
know that proteins have numerous roles inside the organism’s cells including catalyzing
reactions, cellular infrastructure, cell-to-cell signaling, and cellular processes such as DNA
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replication, and even transcription and translation. The pre-instructional interviews revealed that
students lacked an understanding of the role of proteins. Of the 12 students, 10 students
described the function of proteins from a dietary perspective: vital for health, needed for
strength, or for nutrition. Only one student described the role of proteins at a cellular level,
stating that cells are made up of proteins and that proteins help rebuild genes. When asked about
the role of proteins during the post-instructional interviews, the students’ answers became more
diverse and shifted towards the cellular level (Table 3). Students gave responses such as: do
everything in the body, responsible for different reactions, maintain the body, slow down cell
division, DNA repair, eye color, and hair color. Three students were not able to describe any
function of proteins. Although many of the students could give vague examples of cellular
functions for proteins, they still could not explain the importance of proteins in living systems
and give concrete examples to demonstrate this importance.
Target concept 3: each cell contains the entire genome and gene expression.
The pilot study and pre-instructional questionnaires revealed that many students thought
specialized cells, such as muscle and nerve cells, have only the genes they needed to perform
their specialized functions. Based on these findings, Author B designed instruction to confront
this alternative conception. Target Concept 3 had two components: (a) within an organism, each
cell contains the entire genome; and (b) genes are turned on and off, rather than being
continuously expressed. Table 4 shows the students’ pre- and post-instructional understandings
of this target concept.
--------------------------------------------------------------------------------------Insert Table 4 here
--------------------------------------------------------------------------------------
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In the pre-instructional questionnaire and the initial interview, students were asked to
respond to two statements: (a) A muscle cell has only the genes needed to function as part of a
muscle; and (b) A skin cell has genes for eye color (See Appendix, Questions 9 and 10). The
majority of the students (9 of the 12) indicated that specialized cells have only the genes they
need to perform their specialized functions. In the pre-instructional interviews, only one student
understood that each cell contains the entire genome, and none of the students used the concept
of gene expression in their explanations.
In the post-instructional interviews, 10 students stated that each cell contains the entire
genome for that organism, while 2 students held on to the alternative conception that specialized
cells have only the genes they need. These 10 students also used the concept of gene expression
in their explanation. Below is a typical student’s response in the post-instructional interview:
I:
Let’s go to Questions 9 and 10. Question 10 states, ‘A skin cell would have genes
for eye color. ‘
CK:
And I put [referring to pre-test response] that I disagreed. But I was wrong. It
should be strongly agree, because they all contain the same genes.
I:
And then going back to Question 9 which states a muscle cell has only the genes
to be a muscle. And you agreed on the pre-test-
CK:
Yeah. But now I strongly disagree, because they contain all the same genes.
I:
And what then makes the skin and the muscle different?
CK:
Gene expression?
I:
OK. What does that term mean to you?
CK:
Just that different genes are turned on and off based on where they are. So they
know what they’re supposed to be doing. Like, I have a skin cell and it knows it’s
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supposed to be a skin cell. It’s just going to show the DNA for a skin cell even
though it has all of the other ones (CK, 2nd interview, pp 5-6).
In the post-instructional interview, the students were asked to explain a diagram that
illustrated the process of cloning Dolly (see Figure 3). The purpose of the interview task was to
ascertain the status of the student’s conception, whether they found the target concept fruitful in
their explanation. After the interviewer gave an overview of the cloning diagram, students were
asked to explain the source of all of the DNA needed to create Dolly. The 10 students who held
the conception that each somatic cell contains the entire genome had no difficulty explaining the
source of the DNA needed to create Dolly, as illustrated in the interview excerpt below:
I:
This donor cell was a specialized cell that produced milk. Where did the donor
cell get the rest of the instructions to make an entire sheep?
MH:
OK. So, a cell contains all of the genes, but just not all of them are used for
certain cells. Like, you know, just the genes used to produce proteins that make
milk or whatever are used in this cell. But all the DNA is there, but it’s just not
used in that specialized cell.
I:
OK. So, with that line of reasoning, does this cloning diagram seem possible?
MH:
Yeah. I think so (MK, 2nd interview, p. 12).
After instruction, two students held on to the alternative conception that cells have only the genes
they need to function. One student, BN, was consistent in his responses during the second
interview; he thought that cells had only the genes they needed to function. At the end of the
interview, the student was asked to explain the sheep cloning diagram. The student spent a
considerable amount of time thinking about the diagram, and asked numerous questions. The
student eventually reasoned that the donor mammary cell must contain the entire sheep genome.
Examining Students’ Conceptions
21
However, this student lacked the idea of gene expression. The student was experiencing
disequilibrium, as illustrated in the following interview excerpt:
BN:
[Asking questions about the diagram] And then from the black sheep we had?
I:
Just cytoplasm in the cell [from sheep 2].
BN:
Just the cytoplasm with the nucleus taken out. And these two were fused. So, if
nothing else was added, then that’s possible. Even though it’s a specialized cell,
it still had the DNA and the genes throughout the sheep’s whole body to make
Dolly, a clone, so…I guess back here…I guess I would change my answer, I
guess. I don’t know. I’m confused on relating these two together [Questionnaire
#9 and #10 and the cloning diagram]. So, I guess I disagree with it. Is that what
I’m saying? I’m confused.
I:
What about Question 10? Do you want to change your answer?
BN:
[Reading Question 10] ‘A skin cell has genes for eye color.’ See, I don’t agree
with that. Just because, if you go into your skin, it doesn’t have the genes for your
eye color, too. Does it? I want the real answer (BN, 2nd interview, pp. 10-11).
The student began to express dissatisfaction with his original conception that cells contain only
the genes they need to function. However, the student lacked the concept of gene expression,
making the scientific conception seem implausible.
Molecular Genetics Instruction
At the beginning of the semester, Author B elicited students’ prior conceptions by asking
students to complete a pre-instructional questionnaire (see Appendix A). As Author B designed
her instruction for the genetics unit, she used the questionnaire responses to guide her instruction.
Examining Students’ Conceptions
22
Author B’s instructional artifacts, primarily PowerPoint presentations, were analyzed and are
described below, organized around each of the three target concepts.
Target concept 1: DNA, genes and chromosomes.
The pilot study and pre-test responses indicated that the majority of the students did not
understand the physical relationship between DNA and chromosomes, and did not think of genes
as physical entities. To help students gain an understanding of the physical relationships
between DNA, chromosomes, and genes, Author B used visual diagrams and analogies to make
the relationships explicit. She then asked students to test out their ideas by creating their own
analogies to explain the relationship between DNA, chromosomes and genes.
At the beginning of the genetics unit, Author B asked students the following question:
“What do you picture when I say each of these terms: genes, DNA, chromosome and genome?
(Slide 37, Lecture 12, F03) She showed images of common student responses, such as a pair of
blue jeans for the term, “gene” (see Figure 4). Author B used this strategy to elicit students’
prior ideas of these genetics terms. To help students understand the physical relationship
between these terms, Author B organized the first genetics lecture around the following three
questions: “What is the structure of DNA? What is a chromosome? What is a gene?”(Lecture
12, F03). After explaining the structure of a DNA molecule, Author B used a visual diagram that
illustrated the physical relationship between DNA and chromosomes (see Figure 5). Author B
divided the diagram into sections, first focusing on the DNA helix, then on the DNA wrapping
around histones, and finally on the coiling and supercoiling of the DNA to form a chromosome
(Slides 34-36, Lecture 12, F03). As Author B moved from one structure to the next in the
diagram, she discussed issues related to scale. After using this diagram to show the physical
relationship between DNA and chromosomes, Author B returned to the double helix structure to
Examining Students’ Conceptions
23
illustrate the physical structure of genes (Slides 44-46, Lecture 12, F03). To illustrate the length
of a typical gene sequence, Author B showed the sequence of the Arabidopsis NPH4 gene, which
is the focus of her research.
Author B used metaphors and analogies to help students’ develop conceptual
understanding of the target concept. To explain the size relationship between a DNA molecule
and chromosomes, Author B used the analogy of packing people inside a Volkswagon Beetle,
comparing this to 7,000,000 microns of DNA being packed into a single cell of 10 microns in
diameter. Author B used the analogy of a cookbook to explain the relationship between genes,
chromosomes, DNA and genome (Slides 79-84). Students were then asked to work in small
groups to create their own analogies (Slide 86, Lecture 12, F03). Author B selected several
groups to share their analogies with the class (see Table 5). Author B facilitated a class
discussion, asking the students to analyze the selected analogies for strengths and weaknesses in
regard to structural and functional relationships. As a follow-up homework assignment, Author
B gave additional examples of student-generated analogies, again asking the students to critically
analyze the relationships in the analogies.
Target concept 2: gene function and role of proteins.
To help students understand the relationship between genes and proteins, Author B
showed how genes code for proteins through the processes of transcription and translation.
Students transcribed a short DNA sequence into the mRNA sequence, and then translated the
mRNA into an amino acid sequence. Author B altered the original gene sequence and illustrated
how mutations may or may not change the resulting protein. Sickle cell anemia was used as a
case study to further illustrate the effect of mutations on proteins.
Examining Students’ Conceptions
24
The instructor concluded the protein synthesis discussion by stating that all the steps in
transcription and translation required proteins (for example: RNA polymerase). Working in
small groups, students were asked to discuss the following question, “Where do these helper
proteins come from?” The first four groups who shared the results of their discussion offered
incorrect or incomplete responses (examples: the food we eat, from cells dividing, from the
parents, and from amino acids). The fifth group to respond offered the following explanation,
“they are made from information in the genes and are made from transcription and translation.”
Author B probed the students’ understanding by asking, “What causes one person to have blue
eyes and another person to have brown eyes?” Students quickly responded that different eye
colors are caused by different versions of the eye color gene (alleles were discussed earlier in the
course, but students’ conceptions of alleles are not reported in this paper). Returning to their
small groups, students were given the following question, “We have decided that all cells have
the same DNA, but what gives color to eye cells?” Students responded that a protein produced
in the eyes was responsible for eye color, and that different versions of the gene determined what
type of protein was produced. Author B returned to the cookbook analogy in designing the next
small group assignment. Students were asked to use the analogy of an apple pie recipe to explain
the relationship of genes and proteins, as well as the effects of mutations.
Target concept 3: each cell contains the entire genome and gene expression.
From the pilot study and responses to the pre-instructional questionnaire, Author B knew
the majority of the students thought specialized cells, such as muscle and nerve cells, had only
the genes they needed to be specialized (See Table 4). Students also lacked the concept of gene
expression. The majority of students thought that if a cell had a specific gene, for example, an
eye color gene, that the cell would exhibit that particular trait.
Examining Students’ Conceptions
25
In the molecular genetics unit, Author B revisited several items on the pre-test. She
asked the students to consider the following question, “Does a skin cell have the genes for eye
color?” (Slide 89, Lecture 12, F03). Students first discussed their ideas in small groups of 3 – 4
students. Students were given a limited amount of time for their small group discussions, and
Author B randomly chose several small groups to summarize their discussion for the entire class.
The use of small group discussions allowed students’ ideas to be an explicit part of the discourse
in the class. After eliciting students’ ideas, Author B confronted the students’ alternative
conceptions. In small group discussions, Author B asked students to explain how it was possible
to use DNA fingerprinting to identify victims from the World Trade Center site. Author B then
introduced the scientific explanation that each cell in an organism contains the entire genome,
and that different cells express different genes.
Author B organized the DNA replication and mitosis lectures around the guiding
question, “How is it that every cell has the same DNA?” (Slide 13, Lecture 13, F03). At the end
of the protein synthesis lecture, students discussed the following question in small groups, “What
makes skin cells different from muscle cells?” (Slide 39, Lecture 17, F03). After the small group
discussion, Author B presented a simple overview of gene switches, including the role of
repressor and enhancer proteins. (Slides 44-47, Lecture 12, F03) She showed a drawing of a
chromosome that included the amylase gene, which codes for a digestive enzyme, and the
SynCAM gene, which codes for a protein that forms nervous tissue connections (see Figure 6).
Students were asked, “Which gene would cells in your mouth express?” and “Which gene would
a nerve cell express?” In small group discussions, students were able to test the plausibility and
fruitfulness of the conception that cells contain the entire genome. Author B gave additional
Examining Students’ Conceptions
26
examples of specific genes that are only expressed during human embryonic development, such
as the “Tinman” genes, master genes involved in the development of the heart.
Discussion and Teaching Implications
Target Concept 1: physical relationship between DNA, chromosome, and gene
The pre-instructional questionnaires and interviews (See Tables 1 and 2) revealed that
none of the students could accurately describe the physical relationships between DNA,
chromosomes and genes. These findings are confirmed by other researchers (e.g., Banet &
Ayuso (2000) in a study of secondary students in Spain; Stewart (1982, 1983) in a study of
secondary students in the United States; Wood-Robinson et al. (2000) and Lewis & WoodRobinson (2000) in a study of secondary students in the U.K.; and Marbach-Ad (2001) in a study
of secondary students in Israel). In this study, none of the 12 students could accurately describe
the physical relationship of a gene in relation to DNA or a chromosome.
Based on the information from the pre-instructional questionnaire and interviews, Author
B organized her lectures to explicitly teach the physical relationship between chromosomes,
DNA and genes. Other researchers have made this recommendation based on studies showing
students’ confusion (e.g., Kinnear, 1992; Lewis, Leach & Wood-Robinson, 2000a). Author B
chose to begin with a discussion of DNA, drawing on the students’ initial understanding of a
ladder-like structure. She elaborated on the components of the DNA molecule, and then
connected the DNA molecule to the structure of a chromosome. Author B returned to the
familiar double helix structure to introduce genes. Through the analysis of student-generated
analogies, students constructed their understanding of the physical and functional relationships
between DNA, genes and chromosomes.
Examining Students’ Conceptions
27
In the post-test interview, 7 of the 12 students gave detailed explanations of the physical
relationship between DNA and chromosomes, including the role of histones. Of the remaining 5
students, 3 students stated that DNA makes up chromosomes but could not be more explicit
about the relationship. Ten students stated that genes were sections of a chromosome or that
chromosomes contained genes. Of the 12 students, 7 students identified genes as a section of
DNA. Based on the post-instructional interviews, the findings of this study indicate that explicit
teaching of the physical relationships between chromosomes, DNA and genes does help students
acquire accurate understandings.
Implications for teaching.
We recommend sequencing instruction to discuss DNA, genes and chromosomes in
relationship to each other, rather than the typical textbook sequence of including DNA structure
with other organic compound, later discussing chromosomes in the context of cell division and
discussing genes only with respect to traits and Mendalian genetics. When making the physical
relationships explicit, instructors should also note any changes in scale in the visual
representations used in the lecture and text. After making the relationships explicit, students need
opportunities to construct their own understandings. In this study, the use of student-generated
analogies and follow-up analysis appeared to support the development of students’
understandings of the relationships between structures.
Concept 2: gene function and role of proteins.
First-year university students (non-science majors) self-report that they are not confident
in their definition of genes (Bahar et al., 1999). In this study, when students were asked to
describe genes in the initial interview, 10 students equated genes with traits or as a source of
traits. None of the students described genes as coding for proteins. Lewis & Kattmann (2004)
Examining Students’ Conceptions
28
report secondary students describing genes as a small particle bearing a trait or characteristic.
Marbach-Ad and Stavy (2000) describe a similar finding in that 9th grade Israeli students equated
genes with traits or genes being composed of traits, and 12th grade students describing genes as
determining traits. Lewis et al. (2000a) in their large-scale study of secondary British students
concluded, “What they [the students] appeared to lack was a basic understanding of what a gene
is – its basic function, where it might be found, and how it relates to other structures (pp. 76-77).
Students entered the introductory biology course with no clear understanding of the
relationship between genes and proteins. Duncan and Reiser (2003) report similar findings in
their study of 10th grade students. In our study, some students stated that genes are responsible
for traits, but could not offer any mechanism for this. This finding agrees with Lewis et al.
(2000a) in which they asked 14-16 year olds in the UK, “Why are genes important?” “Seventythree per cent of the students responded to the question indicated determination of characteristics
and 14 % indicated transfer of information. None referred directly to a gene product” (p.75).
Author B’s goal was for students to draw a connection between genes and traits that
included the functional importance of proteins. With that connection in place, Author B thought
students should then be able to explain how mutations can result in genetic disorders and
understand the importance of proteins in cellular function. Towards this end, Author B
developed a series of lectures that demonstrated the mechanics of using the information stored in
DNA to make a unique protein and showed that changing the DNA sequence could change the
protein and possibly the protein’s function.
In the post-instructional interviews, 8 students expanded their definitions of genes to
include the definition of genes as coding for a protein. Venville and Treagust (1998) suggest that
students’ thinking about genes undergoes ontological changes, progressing from genes as passive
Examining Students’ Conceptions
29
particles to a gene as active particles to genes as a sequence of instructions to genes as a
productive sequence of instructions (p. 1040). Although we did not specifically use this model
in our analysis, the data indicated that many students shifted from the idea of genes as a passive
particle to genes as a sequence of instructions. However, few of the students appeared to move
to the idea of genes as a productive sequence of instructions. When asked to explain how a
specific protein, hemoglobin was made, 9 students responded that they had no idea.
In regard to the role of proteins in the body, students’ ideas shifted from a dietary
perspective to a more general perspective of proteins “doing everything in the body.”
Only 3 of the 12 students could list two or more examples of protein function on a cellular level.
After instruction, 5 students could not give any functions of proteins. Duncan and Reiser (2003)
also found that “students are not very familiar with proteins as functional biological entities” (p.
11). Based on the post-instructional interviews, students appeared to struggle with the
relationship between genes and proteins, and the role of proteins. Duncan and Reiser (2003)
suggest that students find molecular genetics difficult because of the nature of the reasoning
required. Students are required to reason across a hybrid hierarchical system: an information
level (the gene) and the structure-function level (proteins). Duncan and Reiser found that
students are capable of this type of reasoning, but recommend a greater instructional focus on
“the functions of proteins and their role in mediating genetic effects” (p. 20).
Implications for teaching.
Students’ understandings of genes and the role of proteins fell short of meeting Author
B’s goal. This complex target concept will continue to be an area of inquiry for us as instructors.
As we begin to focus our attention to better understanding our students’ difficulties and to try
new instructional strategies, we offer limited implications for teaching at this time. Lewis and
Examining Students’ Conceptions
30
Kattmann (2004) suggest using the sickle cell anemia example to illustrate the link between a
gene, the structure/function of a gene product and the resulting phenotype. Author B followed
this recommendation but with limited success in terms of student understanding of the role of
genes and proteins. Findings from this study suggest that students may need multiple examples,
not just a single example using sickle cell anemia or cystic fibrosis. As college instructors, we
suspect that many of our students “tune out” when we use case studies of sickle cell anemia or
cystic fibrosis, as many high school teachers use these same examples. New video case studies
are needed that illustrate the story line of a mutated gene, altered protein structure and the
resulting effect at the level of the cell, organ, system and organism. Although Author B designed
some small group discussions to allow students to test their ideas about genes and proteins, the
findings from this study indicate the need to expand these opportunities.
Concept 3: Somatic cells contain the entire genome and gene expression
From the pilot study and the pre-instructional data, Author B realized the majority of her
students held an alternative conception, that cells contain only the genes they need. Similar
findings have been documented by other researchers (e.g., Lewis et al., 2000b, in a study of 14 16 year-old British students and Banet & Ayuso, 2000, in a study of 15 -17 year-old students in
Spain). In the pre-instructional interviews, students did not include gene expression and
regulation as part of their explanations. Lewis et al, (2000b) found that British secondary
students lacked the notion of gene switches. Lewis and Kattmann (2004), comparing a study of
secondary-level British students and a similar group of German students, suggest that students
lack an intuitive conception of gene switches. “In the absence of such a notion, they
conceptualize the gene as being expressed continuously. The logical conclusion is that cells
must only contain the genes they need in order to produce the required phenotype” (pp. 203-
Examining Students’ Conceptions
31
204). Lewis et al. (2000b) and Lewis and Kattmann (2004) recommend the instructors explicitly
teach students that genes are turned on and off. Author B, based on her analysis of student
responses on the pre-instructional questionnaire and interviews, reached the same conclusion.
This study is significant because it documents the success of an earlier teaching
recommendation – explicit teaching about genes being turned on and off (Lewis et al., 2000b;
Lewis & Kattmann, 2004). Author B elicited students’ ideas prior to presenting the scientific
explanation that cells contain the entire genome and genes are turned on and off. She then
designed small group discussion questions that allowed students to test out their ideas in a
variety of situations. Of the 12 students interviewed in this study, 10 students had restructured
their ideas, finding the scientific explanation fruitful in explaining the cloning diagram.
Teaching implications.
We make two recommendations for addressing the commonly held alternative conception
that cells contain only the genes they need. First, we confirm an earlier recommendation to
explicitly teach that genes are turned on and off. When students are presented with the
explanation that cells contain the entire genome, this explanation should include the concept of
gene expression or gene switches. Secondly, we recommend that college instructors incorporate
small group discussions within the large lecture format. Small group discussions allowed
students’ ideas to be part of the discourse of the class, even within a class of approximately 300
students. We recommend that instructors provide focus questions for the small group
discussions that challenge students’ alternative conceptions. In this course, a discussion of the
use of DNA fingerprinting to identify victims of the World Trade Center was used to confront
students’ alternative conceptions. We also recommend the use of small group discussions to
allow students to test out the status of newly introduced scientific explanations. We found a
Examining Students’ Conceptions
32
discussion of a cloning diagram to be useful in allowing students to test the fruitfulness of the
conception that each cell contains the entire genome.
Conclusion
This study had two important outcomes. First, we were able to assess our introductory
biology students’ initial understandings of molecular genetics. Based on those findings, we
designed instruction to confront their alternative conceptions and support conceptual
understanding of the target concepts. Through post-instructional interviews, we were able to
examine the effectiveness of our teaching practice. The second outcome of this study was the
pairing of a university instructor with little education training – common in college classrooms –
with an educational researcher. This rewarding collaboration allowed the instructor to learn
methods for effective instruction within the framework of something familiar to a bench
scientist: research. We hope to continue this collaboration to investigate other questions and
encourage others to form similar collaborations in their institutions.
Examining Students’ Conceptions
33
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Appendix
Questionnaire
Name:
Student #:
Signature:
Major:
List the science classes you have taken in
a) high school:
b) college:
Please answer the following questions to the best of your ability. This is a pretest, so you will
not be graded on your accuracy, but you will be graded on your effort.
1) What is a gene?
2) For each statement, circle if the statement is true or false and explain.
a) A chromosome is larger than a DNA molecule.
Explain:
True
b) One DNA molecule can contain many genes.
Explain:
c) One gene contains many chromosomes.
Explain:
False
True
True
False
False
3) Explain the relationship between DNA and a chromosome (use drawings if you find them
helpful!).
4) Explain the relationship between DNA and a gene (use drawings if you find them helpful!).
5) In a single cell, which would there be more of: chromosomes or genes? Explain your answer.
6) Is the DNA in a single skin cell different from the DNA in a single muscle cell? Explain your
answer.
7) What is an allele?
Examining Students’ Conceptions
39
For questions 8-11, please score the following statements from 1-5 depending on how much you
agree with that statement, circle your choice and explain your answer:
8) A fertilized human egg has all the DNA (and genes) to form a baby.
[strongly agree]
1
2
3
4
5
[strongly disagree]
Explain:
9) A muscle cell has only the genes needed to function as part of a muscle.
[strongly agree]
1
2
3
4
5
[strongly disagree]
4
5
[strongly disagree]
Explain:
10) A skin cell has genes for eye color.
[strongly agree]
1
2
3
Explain:
11) There can be many versions (forms) of a single gene.
[strongly agree]
1
2
3
4
5
[strongly disagree]
Explain:
12) For each statement, circle if the statement is true or false and explain.
a) Two sisters look different from each other because they inherited different genes.
True False
Explain:
b) Two brothers look different from each other because they inherited different versions of the
same genes.
True False
Explain:
13) Explain the relationship between a gene and a protein (use drawings if you find them
helpful!).
14) What roles/jobs do proteins have in your cells?
Examining Students’ Conceptions
40
15) Individuals who have albinism (an inherited disease where the individual has white hair and
skin) have… (circle all that apply):
a) the albinism gene, a gene healthy individuals lack
b) a mutated version of the albinism gene
c) a protein that does not work properly
Explain your choice(s) on what you circled (use the back if necessary):
16) A change in the gene sequence … (circle all that apply):
a) is a new version of the gene
b) is called a mutation
c) can cause a different protein to be made, one that will still work properly.
d) can cause a different protein to be made, one that will no longer work.
e) may not change the protein made
Explain your choice(s) on what you circled:
17) Hemoglobin is a protein in your red blood cells. How do your cells make this protein?
Examining Students’ Conceptions
41
Table 1
Concept 1: Students’ pre- and post-instructional understandings of the physical structure of
DNA and chromosomes (N = 12)__________________________________________________
Subconcepts____
Pre-
Post- ________________________
DNA
Double helix w/bases
0
6
Double helix/ladder structure
8
5
Chain of chromosomes
1
0
Didn’t know
3
1
DNA + histones
0
7
DNA makes up chromosomes
0
3
Replicated chromosome
1
0
Only X and Y chromosomes
4
0
Thread-like structures
2
0
Chromosomes inside DNA molecule
4
0
Didn’t know
2
2
Chromosome
Note: In some cases, students gave multiple answers.
Examining Students’ Conceptions
42
Table 2
Concept 1: Students’ pre- and post-instructional understandings of the relationship between
DNA, chromosomes and genes (N = 12)_____________________________________________
Subconcepts____
Pre-
Post- ________________________
Gene: a section of DNA
0
7
DNA made up of genes
0
1
Gene: rung on double helix
1
2
Didn’t know
11
1
Gene = section of a chromosome
0
5
Chromosomes contain genes
0
5
Genes contain many chromosomes
0
1
Gene: centromere of chromosome
1
0
Didn’t know
11
1
Histones + DNA
0
7
DNA makes up chromosomes
0
3
Chromosomes: rung of double helix
3
0
Didn’t know/Lack of evidence
9
2
Gene and DNA
Gene and chromosome
DNA and chromosome
________________________________________________________________________
Examining Students’ Conceptions
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Table 3
Concept 2: Students’ pre- and post-instructional understandings of gene function and the role of
proteins (n = 12)_______________________________________________________________
Subcomponents
Pre-
Post-_________________________
Gene Function
Codes for protein
0
8
Stores information
2
0
10
7
Genes code for proteins
1
8
Proteins give fuel to genes
1
0
10
4
0
3
12
9
Responsible for cellular function
0
4
Cells are made of proteins
2
0
10
4
One specific example
0
3
2+ specific examples
0
3
Didn’t know
2
5
Source of traits
Relationship between genes and proteins
Didn’t know
Hemoglobin production
Hemoglobin gene is read
Didn’t know
Role of proteins
Health, energy, strength
______________________________________________________________________
Examining Students’ Conceptions
Note: In some instances, students held multiple conceptions.
44
Examining Students’ Conceptions
Table 4
Concept 3: Students’ pre- and post- instructional understandings of each cell containing the
entire genome and gene expression (N = 12)_________________________________
Subconcepts
Pre-
Post-___________________________
Cells contain entire genome
1
10
Cells have only genes they need
9
2
Didn’t know
2
0
Could explain
-
11
Could not explain
-
1
Genes are turned on and off
0
10
Didn’t know/No evidence
12
2
Entire genome in every cell
Application: cloning Dolly
Gene expression
________________________________________________________________________
Note. In the pre-instructional interview, the cloning diagram was not included in the interview
protocol.
45
Examining Students’ Conceptions
Table 5
Target Concept 1: Analogies_________________________________________________
Structures
Instructor
Student Example
Genome
entire cookbook
National Football League
Chromosomes
meat section
teams (players plus coaches)
DNA
all the text
all the players
Gene
meatloaf recipe
specific player on a team
46
Examining Students’ Conceptions
47
Figure Captions
Figure 1. Student drawing of the relationship between DNA and chromosomes
Figure 2. Alternative Model of DNA molecule
Figure 3. Diagram used to demonstrate the cloning of Dolly (Krogh, 2002, p. 299)
Figure 4. Slide used to confront images students commonly have when one the terms
“gene”, “DNA”, “Chromosome” and “Genome”(Slide 37, Lecture 12, F03)
Figure 5. Slides used to explain the relationship between DNA and chromosomes
(Slides 34-36, Lecture 12, F03)
Figure 6. Illustration of the idea that all cells have the same genes but only use some of
them (Slides 44-47, Lecture 12, F03)
Examining Students’ Conceptions
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Examining Students’ Conceptions
49
Examining Students’ Conceptions
gene
chromosome
DNA Molecule Sketch
50
Examining Students’ Conceptions
51
Examining Students’ Conceptions
52
Examining Students’ Conceptions
53
Examining Students’ Conceptions
54
Examining Students’ Conceptions
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