Chapter 01
Overview of
Genetics
Genetics – Overview
• Genetics is the study of heredity and variation
• 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
2
Genetic Discoveries and Technology
• Genetic discoveries are growing at a fast pace
• Example: The Human Genome Project
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
3
Chromosomes
DNA, the molecule of life
Cell
Trillions of cells
Each cell contains:
• 46 human chromosomes,
found in 23 pairs
Gene
G
T A
T A
A T
• Approximately 20,000 to 25,000
genes coding for proteins that perform
most life functions
C G
A T
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
• 2 meters of DNA
DNA
mRNA
Amino acid
Protein (composed of amino acids)
4
Genetic Technology
• New genetic technologies are useful and sometimes
controversial
• 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
5
• Mammalian cloning
o
o
o
o
1997, Dolly the sheep was cloned
2002, Carbon copy (or “Copycat”)
Cloned livestock could benefit farmers
Human cloning has been legally banned
6
• Green fluorescent protein (GFP)
o
o
o
o
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
o Could be used to select sterile males for malaria
control programs
7
1.1 The Molecular Expression
of Genes

Biochemical composition of cells

How DNA stores the information to make proteins

Proteins are largely responsible for cells structure and
function
8
Genes and Traits
• Geneticists study the relationship between genes
and traits
• Trait – any characteristic that an organism displays
• During growth and development, genes provide a
blueprint that determine the organism’s traits
• Examples of human traits:
o
o
o
o
Eye color
Hair texture
Height
Blood Type
9
Living Cells are Composed of Biochemicals
• All cells are constructed from small organic
molecules
• These are linked together by chemical bonds to
form larger molecules
• Cells contain four main types of large molecules
o
o
o
o
Nucleic acids
Proteins
Carbohydrates
Lipids
10
• Nucleic acids, proteins and carbohydrates can form
macromolecules
o Polymers constructed from smaller molecules
• Cellular structures form as a result of the interaction
of molecules and macromolecules
• Organelle – a membrane-bound compartment with
a specialized function
o ex: nucleus
11
Proteins Determine Cell Structure and Function
• The characteristics of a cell depend on its proteins
• Proteins are the “workhorses” of cells
• They have diverse biological functions
o
o
o
o
Transport
Motor proteins
Signaling
Enzymes – proteins that speed up chemical reactions
12
DNA Stores the Information for Protein Synthesis
• The genetic material in most living organisms is
deoxyribonucleic acid (DNA)
• 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
13
• Each nucleotide contains one nitrogenous base
•
•
•
•
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
• Genetic information is stored in the linear sequence of
bases
• Genes – segments of DNA that produce a functional
product
o The fundamental unit of heredity
o Information in genes directs production of proteins
14
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
15
• The DNA in living cells is contained
within large structures termed
chromosomes.
• 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
16
DNA Information is Accessed During
the Process of Gene Expression
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
RNA (messenger RNA)
Translation
Protein
(sequence of
amino acids)
Functioning of proteins within living
cells influences an organism’s traits.
17
1.2 The Relationship Between Genes
and Traits





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
18
Traits
• Trait – any characteristic that an organism displays
• Morphological traits
o Affect the appearance of the organism
o Example: The color of a flower
• Physiological traits
o Affect the function of the organism
o Example: Ability to metabolize a sugar
• Behavioral traits
o Affect the ways an organism responds to the environment
o Example: Mating calls of bird species
19
Molecular Expression of Genes Leads to
an Organism’s Traits
• The relationship between genes and traits spans
four levels of biological organization:
o Molecular level
• Transcription and translation produce proteins
o Cellular level
• Proteins function within the structures of the cell
o Organism level
• Traits seen at the organism level arise from molecular and
cellular properties
o Population level
• Species traits are selected based on survival and
reproduction
20
Example: Dark and Light Butterflies
• Molecular level
o The pigmentation gene exists in two different alleles – variant
forms of a gene with different sequences
• Cellular level
o One version of the pigmentation enzyme functions well;
the other enzyme functions poorly
• Organism level
o Butterflies with much pigment look dark; little pigment look light
• Population level
o Light or dark butterflies are selected in different environments
21
The relationship between genes and traits spans
four levels of biological organization
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Pigmentation gene,
dark allele
Pigmentation gene,
light allele
Pigment
molecule
Transcription and translation
Wing cells
Lots of pigment made
Highly functional
pigmentation enzyme
Poorly functional
pigmentation enzyme
Little pigment made
b. Cellular level
a. Molecular level
Dark butterfly
Light butterfly
c. Organism level
Dark butterflies are usually
in forested regions.
Light butterflies are usually
in unforested regions.
d. Populational level
22
Inherited Differences in Traits Are Due to
Genetic Variation
• Genetic variation refers to differences
in inherited traits among individuals
within a population
o Ex: White vs. purple flowers
o Ex: Black vs. brown hair
• 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
23
• Genetic variation results from different kinds of
changes at the molecular level
o Gene mutations
• Heritable changes in gene sequence
• One nucleotide change can have big effect
o Changes in chromosome structure
• Large segments of the chromosome may be lost
or rearranged
o Changes in chromosome number
• One chromosome lost of gained
• Whole set of chromosomes lost or gained
24
Traits Are Governed by Genes
and the Environment
• Traits cannot be explained by genes alone
• Traits result from the interaction between genes and
the environment
o
o
o
o
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
25
• Phenylketonuria (PKU)
o Phenylalanine hydroxylase enzyme
• Converts phenylalanine to tyrosine
o Humans need one or two functional copies of the gene to metabolize
phenylalanine
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
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
26
During Reproduction, Genes are Passed
from Parent to Offspring
• Gregor Mendel, in the mid-19th century, provided
the foundation for the science of genetics
• He described the basic principles of inheritance
• Inheritance is explained by the behavior of
chromosomes during cell division
27
• Sexually-reproducing species are diploid
o Two copies of each chromosome, one from each parent
o Homologs – the two copies of each chromosome
• 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
28
• 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
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
XX
Reproductive Cell
(gamete)
• Sexual reproduction enhances
genetic variation
o Creates new combinations of traits not found
in either parent
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16
17 18 19 20 21 22 X
29
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
Hippidium
and other genera
0
Nannippus
Pliohippus
Hipparion Neohipparion
Stylohipparion
5
10
o This is called biological evolution
Sinohippus
Megahippus
Calippus
Archaeohippus
20
• 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
Parahippus
Miohippus
Mesohippus
40
Paleotherium
Epihippus
Propalaeotherium
Pachynolophus
• Example: Evolution of the
modern horse, Equus
Hypohippus
Orohippus
55
Hyracotherium
•
Important changes:
–
Larger size
–
Fewer toes
–
Modified jaw for
grazing
30
1.3 Fields of Genetics

Transmission Genetics

Molecular Genetics

Population Genetics
31
Geneticists Focus on Model Organisms
• Model organisms – species
studied by many researchers
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
32
Transmission Genetics Explores
Inheritance Patterns
• Examines how traits are passed from parents to
offspring
• 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
• Mendel used genetic crosses
o Breed individuals and analyze traits of offspring
33
Transmission Genetics – Example Questions
• How are chromosomes transmitted?
• What are common patterns of gene inheritance?
• What are unusual patterns of inheritance?
• 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?
• How do viruses proliferate?
34
Molecular Genetics Focuses on
Biochemical Understanding
• The most modern field of genetics
• Deals with molecular features of DNA and how these
underlie gene expression
o Organization, control and function of genes
o Analysis of DNA, RNA and proteins
• 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
35
Molecular Genetics – Example Questions
• What are the molecular structures of DNA and RNA?
• What is the composition of chromosomes?
• How is the genetic material copied?
• How are genes expressed at the molecular level?
• How is gene expression regulated during development?
• What is the molecular nature of mutations?
• How do chromosomes exchange material?
• How have genetic technologies advanced understanding?
• What are the composition and function of genomes?
• What is the relationship between genes and disease?
36
Population Genetics is Concerned with
Genetic Variation and Evolution
• Population genetics deals with the genetic
composition of populations and how it changes over
time and space
• 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
37
Population Genetics – Example Questions
• Why are multiple alleles of a gene maintained in a population?
• 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?
38
1.4 The Science of Genetics

Genetics is an experimental science

Genetic TIPS – problem solving strategies
39
Genetics is an Experimental Science
• Geneticists use two basic scientific approaches –
Hypothesis testing and Discovery-based science
• 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
40
Scientific Process
• The textbook “dissects” experiments into five components
to explain the scientific process:
1.
2.
3.
4.
5.
•
Background information
Hypothesis
Experimental Steps
Raw Data
Interpretation of the data
While reading about experiments, consider alternatives!
Develop your own skills to
•
•
•
Formulate hypotheses
Design experiments
Interpret data
41
Problem-Solving Skills
• In addition to learning foundational knowledge,
develop your problem-solving skills
• The textbook includes Genetic TIPS
o Topic, Information, and Problem-solving Strategy
• Ten strategies are used repeatedly:
•
•
•
•
•
Define key terms
Make a drawing
Predict the outcome
Compare and contrast
Relate structure and function
•
•
•
•
•
Describe the steps
Propose a hypothesis
Design an experiment
Use statistics
Make a calculation
42