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Genetics – Overview
•  Genetics is the study of heredity and variation
Chapter 01
Overview of
Genetics
•  Genetics is the unifying discipline in biology
•  Explains why organisms have certain traits
o  How traits are passed from parent to offspring
o  Relationship between genes and traits
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Chromosomes
DNA, the molecule of life
Genetic Discoveries and Technology
Cell
Trillions of cells
Each cell contains:
•  Example: The Human Genome Project
• 2 meters of DNA
• 46 human chromosomes,
found in 23 pairs
G
T A
A T
C G
A T
• Approximately 20,000 to 25,000
genes coding for proteins that perform
most life functions
T A
T A
T A
C G
• Approximately 3 billion
DNA base pairs per set of chromosomes,
containing the bases A, T, G, and C
C G
o  Goal: Decipher the information in the human genome – the DNA of all our
chromosomes
o  First draft in 2001, completed 2003
o  3 billion nucleotide base pairs
o  Shed light on basic questions about human genes, traits, and possible cures
for disease
Gene
T A
•  Genetic discoveries are growing at a fast pace
DNA
mRNA
Amino acid
Protein (composed of amino acids)
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Genetic Technology
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•  Mammalian cloning
•  New genetic technologies are useful and sometimes
controversial
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1997, Dolly the sheep was cloned
2002, Carbon copy (or “Copycat”)
Cloned livestock could benefit farmers
Human cloning has been legally banned
•  Recombinant DNA
o  Can provide new medicines
o  Example: Human recombinant insulin
•  Synthesized by E. coli that carry human genes
•  Provides insulin for diabetes patients
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•  Green fluorescent protein (GFP)
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1.1 The Molecular Expression A jellyfish gene produces a bioluminescent protein
Under UV light it emits a green glow
2008 Nobel Prize was awarded for the development of this powerful tool
Examples:
•  GFP gene expressed in mice
•  GFP expressed in the gonads of male mosquitoes
of Genes
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Biochemical composition of cells
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How DNA stores the information to make proteins
o  Could be used to select sterile males for malaria
control programs
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Proteins are largely responsible for cells structure and
function
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Genes and Traits
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Living Cells are Composed of Biochemicals
•  Geneticists study the relationship between genes
and traits
•  All cells are constructed from small organic
molecules
•  Trait – any characteristic that an organism displays
•  During growth and development, genes provide a
blueprint that determine the organism’s traits
•  These are linked together by chemical bonds to
form larger molecules
•  Examples of human traits:
•  Cells contain four main types of large molecules
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Eye color
Hair texture
Height
Blood Type
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Nucleic acids
Proteins
Carbohydrates
Lipids
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•  Nucleic acids, proteins and carbohydrates can form
macromolecules
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Proteins Determine Cell Structure and Function
•  The characteristics of a cell depend on its proteins
o  Polymers constructed from smaller molecules
•  Cellular structures form as a result of the interaction
of molecules and macromolecules
•  Proteins are the “workhorses” of cells
•  They have diverse biological functions
•  Organelle – a membrane-bound compartment with
a specialized function
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o  ex: nucleus
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Transport
Motor proteins
Signaling
Enzymes – proteins that speed up chemical reactions
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•  Each nucleotide contains one nitrogenous base
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DNA Stores the Information for Protein Synthesis
•  The genetic material in most living organisms is
deoxyribonucleic acid (DNA)
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
•  Genetic information is stored in the linear sequence of
bases
•  DNA encodes the information required to synthesize
all cellular proteins
o  It is able to do so because of its molecular structure
o  DNA is a polymer of nucleotides
•  Genes – segments of DNA that produce a functional
product
o  The fundamental unit of heredity
o  Information in genes directs production of proteins
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•  The DNA in living cells is contained
within large structures termed
chromosomes.
For example:
•  ATG GGC CTT AGC
•  Met Gly Leu Ser
DNA Sequence
Polypeptide Sequence
•  TTT AAG CTT GCC
•  Phe Lys Leu Ala
DNA Sequence
Polypeptide Sequence
•  Each chromosome is a complex of
DNA and proteins
•  An average human chromosome
contains
o  More than a 100 million nucleotides
o  about 1,000 different genes
•  Human cells have a total of 46
chromosomes
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DNA Information is Accessed During the Process of Gene Expression
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1.2 The Relationship Between Genes and Traits
DNA
•  Gene expression occurs in two steps
o  Transcription
•  The genetic information in DNA is copied into a
nucleotide sequence of ribonucleic acid (RNA)
o  Translation
•  The nucleotide sequence in RNA provides the
information (using the genetic code) to
produce the amino acid sequence of a
polypeptide
Gene
Transcription
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RNA (messenger RNA)
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Translation
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Protein
(sequence of
amino acids)
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Functioning of proteins within living
cells influences an organism’s traits.
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How expression of genes leads to an organism’s traits
Genetic variation
The relationship between genes, traits and the
environment
How genes are transmitted in sexually reproducing
species
The process of evolution
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Molecular Expression of Genes Leads to an Organism’s Traits
Traits
•  Trait – any characteristic that an organism displays
•  The relationship between genes and traits spans
four levels of biological organization:
•  Morphological traits
o  Molecular level
o  Affect the appearance of the organism
o  Example: The color of a flower
•  Transcription and translation produce proteins
o  Cellular level
•  Proteins function within the structures of the cell
•  Physiological traits
o  Organism level
•  Traits seen at the organism level arise from molecular and
cellular properties
o  Affect the function of the organism
o  Example: Ability to metabolize a sugar
o  Population level
•  Species traits are selected based on survival and
reproduction
•  Behavioral traits
o  Affect the ways an organism responds to the environment
o  Example: Mating calls of bird species
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The relationship between genes and traits spans
four levels of biological organization
Example: Dark and Light BuNerflies
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
•  Molecular level
Pigmentation gene,
dark allele
o  The pigmentation gene exists in two different alleles – variant
forms of a gene with different sequences
•  Cellular level
Pigment
molecule
Wing cells
Lots of pigment made
Highly functional
pigmentation enzyme
o  One version of the pigmentation enzyme functions well;
the other enzyme functions poorly
Pigmentation gene,
light allele
Transcription and translation
Poorly functional
pigmentation enzyme
Little pigment made
b.  Cellular level
a.  Molecular level
•  Organism level
o  Butterflies with much pigment look dark; little pigment look light
•  Population level
Dark butterfly
o  Light or dark butterflies are selected in different environments
Light butterfly
c.  Organism level
Dark butterflies are usually
in forested regions.
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Light butterflies are usually
in unforested regions.
d. Populational level
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•  Genetic variation results from different kinds of
changes at the molecular level
Inherited Differences in Traits Are Due to Genetic Variation o  Gene mutations
•  Heritable changes in gene sequence
•  One nucleotide change can have big effect
•  Genetic variation refers to differences
in inherited traits among individuals
within a population
o  Changes in chromosome structure
•  Large segments of the chromosome may be lost
or rearranged
o  Ex: White vs. purple flowers
o  Ex: Black vs. brown hair
o  Changes in chromosome number
•  One chromosome lost of gained
•  Whole set of chromosomes lost or gained
•  In some cases, genetic variation is very
striking
o  Members of the same species may be misidentified as
belonging to different species
o  Morphs – contrasting forms within a single species
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Traits Are Governed by Genes and the Environment •  Phenylketonuria (PKU)
o  Phenylalanine hydroxylase enzyme
•  Converts phenylalanine to tyrosine
•  Traits cannot be explained by genes alone
o  Humans need one or two functional copies of the gene to metabolize
phenylalanine
•  Traits result from the interaction between genes and
the environment
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o  Humans with two copies of a rare inactive allele cannot metabolize
phenylalanine
•  Phenylalanine accumulates, causing a number of detrimental effects
•  Can be mentally impaired
Called the norm of reaction
Ex: Diet has an effect on height, weight and even intelligence
Environment may control whether a genetic disease is manifested
Ex: Phenylketonuria
o  Newborns are now screened for PKU
o  Individuals with PKU are put on a strict diet
low in phenylalanine
o  Controlled diet allows normal development
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During Reproduction, Genes are Passed from Parent to Offspring •  Sexually-reproducing species are diploid
o  Two copies of each chromosome, one from each parent
o  Homologs – the two copies of each chromosome
•  Gregor Mendel, in the mid-19th century, provided
the foundation for the science of genetics
•  Thus two copies of most genes
o  But the two copies may be different alleles
o  Ex: PKU gene is on chromosome 12
o  Only X and Y have some different genes
•  He described the basic principles of inheritance
•  Inheritance is explained by the behavior of
chromosomes during cell division
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•  Most cells of the human body are
somatic cells
with 46 chromosomes
•  Gametes – sperm and egg cells –
are haploid,
with 23 chromosomes
o  Combining sperm and egg during fertilization
restores the diploid number of chromosomes
Somatic Cell
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The Genetic Composition of a Species Evolves Over the Course of Many Generations
•  The genetic makeup of a
population can change
over many generations
Equus
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XX
Reproductive Cell
(gamete)
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Hipparion Neohipparion
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Sinohippus
Megahippus
Calippus
Archaeohippus
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•  Evolution is possible because
of natural selection
o  The process of differential survival and
reproduction based on genes and
traits
o  Genetic changes accumulate over
time
Merychippus
Anchitherium
Hypohippus
Parahippus
Miohippus
Mesohippus
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Paleotherium
Epihippus
Propalaeotherium
Pachynolophus
•  Example: Evolution of the
modern horse, Equus
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Nannippus
Pliohippus
Stylohipparion
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9 10 11 12 13 14 15 16
17 18 19 20 21 22 X
Hippidium
and other genera
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o  This is called biological evolution
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•  Sexual reproduction enhances
genetic variation
o  Creates new combinations of traits not found
in either parent
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Orohippus
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Hyracotherium
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Important changes:
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Larger size
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Fewer toes
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Modified jaw for
grazing
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Geneticists Focus on Model Organisms
•  Model organisms – species
studied by many researchers
1.3 Fields of Genetics
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Transmission Genetics
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Molecular Genetics
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Population Genetics
o  Can compare results
o  Determine principles that could apply to
other species
o  Model species are easy to grow in the lab
•  Examples:
o  Escherichia coli – a bacterium
o  Saccharomyces cerevisiae –
yeast
o  Drosophila melanogaster – fruit fly
o  Caenorhabditis elegans –
nematode
o  Mus musculus – mouse
o  Arabidopsis thaliana – a plant
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Transmission Genetics Explores Inheritance PaNerns
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Transmission Genetics – Example Questions
•  Examines how traits are passed from parents to
offspring
•  How are chromosomes transmitted?
•  What are common patterns of gene inheritance?
•  What are unusual patterns of inheritance?
•  The conceptual framework was provided by Gregor
Mendel in the 1860s
o  Genetic determinants pass from parent to offspring as discrete units
o  Now we know these are genes
•  How is inheritance affected when genes lie on the same
chromosome?
•  How do variations in chromosome structure and number occur?
•  How are genes transmitted by bacteria?
•  Mendel used genetic crosses
•  How do viruses proliferate?
o  Breed individuals and analyze traits of offspring
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Molecular Genetics Focuses on Biochemical Understanding
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Molecular Genetics – Example Questions
•  What are the molecular structures of DNA and RNA?
•  The most modern field of genetics
•  What is the composition of chromosomes?
•  Deals with molecular features of DNA and how these
underlie gene expression
•  How is the genetic material copied?
•  How are genes expressed at the molecular level?
•  How is gene expression regulated during development?
o  Organization, control and function of genes
o  Analysis of DNA, RNA and proteins
•  What is the molecular nature of mutations?
•  How do chromosomes exchange material?
•  Molecular geneticists often use a genetic approach
o  Study mutant genes with abnormal function to infer the normal function of
the gene
•  Example: Loss-of-function mutation
•  How have genetic technologies advanced understanding?
•  What are the composition and function of genomes?
•  What is the relationship between genes and disease?
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Population Genetics is Concerned with Genetic Variation and Evolution
Population Genetics – Example Questions
•  Why are multiple alleles of a gene maintained in a population?
•  Population genetics deals with the genetic
composition of populations and how it changes over
time and space
•  What factors affect prevalence of alleles in a population?
•  What are the contributions of genetics and the environment to
the outcome of a trait?
•  How do genetics and the environment influence quantitative
traits, such as size and weight?
•  Connects genetic variation to the organism’s
environment
o  Allele frequencies are an important type of data
•  It connects the work of Mendel on inheritance to that
of Darwin on evolution
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Genetics is an Experimental Science
•  Geneticists use two basic scientific approaches –
Hypothesis testing and Discovery-based science
1.4 The Science of Genetics
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Genetics is an experimental science
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Genetic TIPS – problem solving strategies
•  Hypothesis Testing
o  Also called the scientific method
o  Allows scientists to validate or invalidate a hypothesis
•  Discovery-Based Science
o  Collecting data without a preconceived hypothesis
o  Ex: Analyzing genes in cancer cells to identify mutations
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Scientific Process
Problem-­‐‑Solving Skills
•  The textbook “dissects” experiments into five components
to explain the scientific process:
1. 
2. 
3. 
4. 
5. 
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Background information
Hypothesis
Experimental Steps
Raw Data
Interpretation of the data
•  The textbook includes Genetic TIPS
o  Topic, Information, and Problem-solving Strategy
While reading about experiments, consider alternatives!
•  Ten strategies are used repeatedly:
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Develop your own skills to
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•  In addition to learning foundational knowledge,
develop your problem-solving skills
Formulate hypotheses
Design experiments
Interpret data
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Define key terms
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Make a drawing
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Predict the outcome
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Compare and contrast
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Relate structure and function • 
Describe the steps
Propose a hypothesis
Design an experiment
Use statistics
Make a calculation
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