Faculty of Science
Freudenthal Institute
for Science and Mathematics Education
problems in defining phenotype and
hereditary trait
Dirk Jan Boerwinkel
Daniel van Draanen
Birgitte Duijts
Amarja Koers
Eridob conference Karlstad 5-9 September 2016
8 september 2016
the concepts of genetic trait and phenotype
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Educational research on genetic trait and phenotype is scarce
These concepts are often ill defined in textbooks (Gericke and
Hagberg, 2010)
Examples in biology education often are limited to outwardly
visible traits in which organisms differ, described on organism or
organ level (Mahner and Kary, 1997; Wood-Robinson et al, 2000)
Understanding of these concepts is vital for understanding the
relations between gene, environment and trait (Gifford, 2000),
and for understanding adaptation (Gould & Lewontin, 1979)
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Are these genetic traits?
1.
2.
3.
4.
5.
6.
7.
A variant in protein structure of a membrane channel
Folding of the neural tube
A DNA profile in forensic DNA research
The performance in a Olympics marathon
The ability to dissimilate glucose
A higher risk on breast cancer
Ability to speak
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Research question
‘to what extent do definitions and meanings of phenotype and
hereditary trait in biology education match with definitions and
meanings in current life sciences research?’
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subquestions
1. Apart from (the sum of) outwardly visible traits in which organisms
differ, which other meanings of genetic trait (and phenotype) can
be derived from literature?
2. To what extent do Biology textbooks cover the different meanings?
3. Which meanings are used and recognized by students in upper
secondary education?
4. Which meanings are used by life science researchers?
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Methods subquestion 1.
Apart from (the sum of) outwardly visible traits in which organisms
differ, which other meanings of genetic trait (and phenotype) can be
derived from literature?
A literature study was done to analyse the different meanings of
hereditary trait and phenotype in literature on the philosophy of
science and academic genetics textbooks from different periods.
These meanings were categorized and compared to the meaning of
variable outwardly visible traits, resulting in a framework.
Churchill, F. B. (1974). William Johannsen and the genotype concept. Journal of the History of Biology, 7(1), 5-30.
Dupré, J. (2012). Processes of life: essays in the philosophy of biology. Oxford University Press. 50
Gericke, N. M., & Hagberg, M. (2007). Definition of historical models of gene function and their relation to students’
understanding of genetics. Science & Education, 16(7-8), 849-881.
Houle, D., Govindaraju, D. R., & Omholt, S. (2010). Phenomics: the next challenge. Nature Reviews Genetics, 11(12), 855866.
Lenartowicz, P. (1975). Phenotype-genotype dichotomy: an essay in theoretical biology.
Mahner, M., & Kary, M. (1997). What exactly are genomes, genotypes and phenotypes? And what about phenomes?. Journal
of Theoretical Biology, 186(1), 55-63.
Violle, C., Navas, M. L., Vile, D., Kazakou, E., Fortunel, C., Hummel, I., & Garnier, E. (2007). Let the concept of trait be
functional!. Oikos, 116(5), 882-892.
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Results subquestion 1.
Apart from (the sum of) outwardly visible traits in which organisms
differ, which other meanings of genetic trait (and phenotype) can be
derived from literature?
The developed framework includes six categories in which traits can
differ from the commonly used examples;
a. non visible traits (versus visible traits)
b. traits on multiple levels (versus traits on organismal level)
c. partially environment-dependent traits (versus environmentindependent traits)
d. traits without variance (versus traits that vary within a population)
e. traits which change during development (versus traits that remain
the same)
f. traits which influence the risk or susceptibility for other traits
(versus traits that are expressed in the phenotype)
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Methods subquestion 2.
To what extent do Biology textbooks cover the different
meanings?
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Analysis of biology textbooks (covering 90% of the books in use)
for upper secondary education (two levels)
Examples of mentioned traits were categorized and the frequency
within the total set of examples was calculated.
Examples were categorized in the framework of trait-meanings
The same example could count in different categories
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Results subquestion 2.
To what extent do Biology textbooks cover the different
meanings?
category
%A
%B
a non visible traits
53
79
b traits on multiple levels
24
27
c partially environment-dependent
16
9
d traits without variance
11
8
e traits which change during development
4
8
f traits which influence the risk
3
3
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Results subquestion 2.
To what extent do Biology textbooks cover the different
meanings?
The concept phenotype is ill defined, both used for the sum of all traits
and for separate traits, and sometimes limited to visible features (‘all
outer observable characteristics belong to the phenotype of an
individual’).
The relation between hereditary trait and phenotype remains unclear
(do acquired characteristics belong to the phenotype?)
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Methods subquestion 3.
Which meanings are used and recognized by students in upper
secondary education?
1. Research group consisted of 150 upper secondary students from
five different schools, which had followed the genetics part of the
biology curriculum.
2. Students were given a questionnaire in which they
• mentioned five examples of hereditary traits
• gave a definition of hereditary trait
• Answered the question whether they considered given examples
of traits in every category of the framework a hereditary trait and
why or why not.
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Questionnaire questions
Format:
Explanation of the trait…
Would you regard this as a hereditary trait?
□ Yes
□ No
□ Not sure
Because
Questions to distinguish category c ‘Traits which are independent from environmental factors
versus traits which are heavily influenced by the environment’
The ability to fold your tongue.
The colour of the human iris.
Natural hair colour
Having a musical talent.
Being good at sports.
Having a high IQ score.
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Results subquestion 3.
Which meanings are used and recognized by students in upper
secondary education?
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Upper secondary school students named in 80 % of the examples
of hereditary traits outer visible, variable and environmentindependent traits.
When confronted with other types of hereditary traits, more than
half of the students had doubts whether these could be considered
as hereditary traits, with exception of the traits on lower
organisational levels (category b).
Arguments to classify a trait as hereditary were mainly whether the
environment influences the trait, in which case the trait was
dismissed as being hereditary.
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Methods subquestion 4.
Which meanings are used by life science researchers?
a. Reviews of genetic research were analysed to distinguish different
types of research in which genetic traits play a role.
b. From each type of research, one scientist was selected, 7 in total
c. Interviews were held in which scientists were asked
• how the concepts phenotype and hereditary trait were used in
their research and whether they differed in meaning.
• whether traits in the categories a to f could be considered
hereditary traits.
d. The results were categorized to compare the different meanings of
phenotype and genetic trait
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Results subquestion 4.
Which meanings are used by life science researchers?
Type of research question
Disciplinary fields
1
To what extent is the variation in trait x
explained by genetic differences?
Trait → genetic?
Twin studies
Behavioural studies
2
Which gene(s) is(are) involved in the
development of this trait?
Trait → which gene?
Medical genetics
3
How is the process from gene expression to
the trait?
Gene → ? → trait
Developmental biology
4
What happens in the cell related to the
expression of the gene?
Gene → ? → molecular process
Molecular and cellular
biology
5
Why and how does a trait change in the
course of evolution
? Change in genes ? → ? change in traits
Evolutionary biology,
environmental genetics
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Results subquestion 4.
Which meanings are used by life science researchers?
Genetic scientists from different fields differed much in their use of the
terms phenotype and hereditary trait.
They agreed that
• the environment always influences a hereditary trait
• Features without variation are not hereditary traits
They disagreed on, doubted on or used inconsequent language on
• Whether a disease is a phenotype
• Whether phenotype and hereditary trait mean the same
• Whether internal features belong to the phenotype
• whether phenotype was used for organism or population level
Some scientists advised not to use hereditary trait as a concept.
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Conclusions
1. The use of the concepts hereditary trait and phenotype is often
confusing and inconsistent, even among scientists.
2. No common definition of phenotype or hereditary trait can be
derived from scientific practice, as different practices have different
use of these concepts.
3. Some scientists advise against the use of hereditary trait as a
concept.
4. Dutch textbooks do give examples of different types of hereditary
traits to a different degree.
5. However, the meaning of hereditary trait in textbooks is still limited
in students’ understanding.
Student understanding of gene-environment-trait relations is probably
hindered by the unclear meaning of hereditary trait.
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Implications for Biology education 1.
The concept of hereditary trait is problematic as
a.As all traits are developed, gene expression always plays a
role
b.The proportion of variance explained by genetic differences
differs gradually and depends on the population
c. Traits without variance are probably the most important and
essential traits of which genetic differences influence fitness
negatively
d.There is an infinite number of traits, depending on what is
the subject of research
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Implications for Biology education 2.
Suggestions for education on traits
1. Use ‘trait’ for any discernible characteristic on any organizational
level.
2. include on any level that traits are the result of the interplay of
many genes and many environmental factors
3. Explain that a trait on organism level is explained/can be described
by traits on lower levels
4. Distinguish between the role of genes and environment in
explaining variation and in realizing the trait.
5. When discussing the genetic component of a trait, always mention
the environmental component and vice versa
6. Do not talk about ‘hereditary traits’ anymore, at the most about
‘traits of which the variation is strongly influenced by differences in
genes’.
7. Explain why ‘hereditary trait’ is not a useful concept as students
will be confronted with these terms
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