BIO 356 – Principles of Genetics
Prereq- BIO 201
Genetics: Analysis and Principles
Robert J. Brooker
CHAPTER 1
OVERVIEW OF
GENETICS
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What is Genetics?
GENETICS – Study of biologically inherited traits
including traits that are partly influenced by the
environment.
GENES – Elements of heredity that are transmitted from
parents to offsprings in reproduction. These are inherited
traits.
Genetics……
• Genetics is the study of inherited traits
• Each organism has its own “Genetic Blueprint”
that makes it different from others.
• This information is stored in the chromosomes
located in the nucleus.
• The genetic information is stored as discrete
instructions called “genes”.
• Their existence was first inferred by Gregor
Mendel in 1866.
History of Genetics
• Serious study of Genetics began in 1902 when the
work of Mendel was rediscovered.
• It was discovered that genes are located on
chromosomes.
• Changes in genes could lead to inherited diseases in
humans (“Inborn Errors of Metabolism”)
• In the next 20 years, methods for gene mapping and
for experimentally inducing mutations were
developed.
History of Genetics contd…
• Starting in 1940, studies using microbes (fungi,
bacteria and bacterial viruses) began.
• Merger of Genetics and Biochemistry led to
“Molecular Genetics”.
• Determination of the Structure of DNA in 1953
led to an explosion in molecular studies.
• During the 1970s, Gene cloning and DNA
sequencing methods were developed.
• Methods for DNA marker analysis, DNA
fingerprinting and Polymerase Chain Reaction
(PCR) were developed in the 1980s.
History of Genetics contd…
• During the 1990s, whole genome sequencing methods
were developed.
• Availability of whole genome sequences led to the
study of all the genes in a genome (Genomics)and of
all the proteins coded by a genome (Proteomics).
• Fusion of Genetics with Computer Science created the
field of “Bioinformatics”
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What better way to start Genetics than
with an overview of the Human Genome
Project?
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Formally launched in 1990
Coordinated by the National Institutes of
Health (NIH) and the Department of Energy
(DOE)
Carried out by scientists from around the
world
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A “working draft” of the human genome
sequence was completed in 2000
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Nearly 3 billion nucleotides
Accuracy greater than 99.99%
The study of the human genome provides
fundamental molecular details
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Figure 1.1a

The knowledge gained from the Human
Genome Project will lead to improvements
in the diagnosis, treatment and prevention
of disease
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Figure 1.1b
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While trying to understand genes and their
function, scientists have developed many
genetic technologies
These genetic technologies are often
controversial
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DNA fingerprinting
Mammalian cloning
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
DNA fingerprinting
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Not well-received at first
Now a common tool of forensic science
Mammalian cloning
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In 1997, Ian Wilmut and colleagues cloned the
first mammal
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A sheep named Dolly (Figure 1.2)
Fears that the technology may be applied to
humans led to legislative bans on human cloning
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Genetic technologies allow the
modification of animals in various ways
For example, mice can be made to glow
green (Figure 1.3)
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A jellyfish gene encoding a green fluorescent
protein (GFP) is introduced into lab mice
Upon exposure to ultraviolet light, the mice
emit a bright green color
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Living Cells Are Composed of
Biochemicals
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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
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Nucleic acids
Proteins
Carbohydrates
Lipids
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Living Cells Are Composed of
Biochemicals
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Nucleic acids, proteins and carbohydrates
are termed macromolecules
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They are polymers constructed from smaller
molecules called monomers
Cellular structures form as a result of the
interaction of molecules and
macromolecules
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Figure 1.4
Each Cell Contains Many Different
Proteins That Determine Cellular
Structure And Function
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The characteristics of a cell largely depend
on the proteins it produces
Proteins are the “workhorses” of cells
They have diverse biological functions
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Structural proteins
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Tubulin
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Contractile proteins
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Myosin
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Aggregates to form microtubules
Plays role in cell shape and movement
Plays role in muscle contraction
Hormonal proteins
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Insulin
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Regulates the level of glucose in the blood
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A particularly important group of proteins
are the enzymes
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Enzymes are biological catalysts
Catabolic enzymes
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Involved in the breakdown of large molecules into
smaller ones
Provide energy for the activities of the cell
Anabolic enzymes
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Involved in the synthesis of large molecules from
smaller ones
Provide components for the construction of the cell
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DNA Stores the Information for
Protein Synthesis
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The genetic material in living organisms is
deoxyribonucleic acid (DNA)
DNA encodes the information required to
synthesize all cellular proteins

It is able to do so because of its molecular
structure
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DNA Stores the Information for
Protein Synthesis
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DNA is a polymer of nucleotides
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Each nucleotide contains one nitrogenous base
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Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
The genetic information is stored in the linear
sequence of these bases along the DNA
molecule
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DNA Stores the Information for
Protein Synthesis
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For example:
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ATG GGC CTT AGC
Met Gly Leu Ser
DNA Sequence
Protein Sequence
TTT AAG CTT GCC
Phe Lys Leu Ala
DNA Sequence
Protein Sequence
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1-19
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The DNA in living cells is contained within
large structures termed chromosomes
Human cells have a total of 46 chromosomes
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Refer to Figure 1.5
Each chromosome is a complex of DNA and
proteins
An average human chromosome contains
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More than a 100 million nucleotides
1000-2000 genes
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The Information Within the DNA
Is Accessed During the Process
of Gene Expression
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Gene expression occurs in two steps
 Transcription
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The genetic information in DNA is copied
into a nucleotide sequence of ribonucleic
acid (RNA)
Translation
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The nucleotide sequence in RNA is
converted (using the genetic code) into the
amino acid sequence of a protein
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Figure 1.6
The Molecular Expression of Genes
Within Cells Leads to an Organism’s
Outwardly Visible Traits
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A trait is any characteristic that an organism
displays
There are two main types of traits
 Morphological traits
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Affect the appearance of the organism
Example: The color of a flower
Physiological traits
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Affect the function of the organism
Example: Ability to metabolize a sugar
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Traits are controlled, at least in part, by
genes
The relationship between genes and traits
spans four levels of biological organization
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1. Genes are expressed at the molecular level
2. Proteins function at the cellular level
3. Traits are observed at the organism’s level
4. Genes/traits within a particular species can
also be studied at the populational level
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Figure 1.7
a. Molecular level
b. Cellular level
c. Organismal level
d. Populational level
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Inherited Differences in Traits Are
Due to Genetic Variation
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Genetic variation refers to differences in inherited
traits among individuals within a population
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In some cases, genetic variation is very striking
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For example: In petunias, white vs. purple flowers
Members of the same species may be misidentified as
belonging to different species
Refer to Figure 1.8 (Garter snakes)
Contrasting forms within a single species are
termed as morphs
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
Genetic variation is a result of various types of
changes at the molecular level
 1. Gene mutations
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2. Changes in chromosome structure
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Small differences in gene sequences
lead to two or more alleles of the same gene
Large segments of the chromosome may be lost or
duplicated
3. Changes in chromosome number
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Single chromosomes may be lost or gained
 Refer to Figure 1.9a (Down Syndrome)
A whole set of chromosomes may be inherited
 Refer to Figure 1.9b (Modern Wheat Plant)
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Traits are Governed by Genes and
by the Environment
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The traits an individual expresses often do
not result from its genes alone
Rather, traits are a result of the interaction
between genes and the environment
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For example, an individual’s diet has an effect
on his/her height and weight
In some cases, the environment dictates
whether a disease is manifested in an
individual or not
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Phenylketonuria (PKU)
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Humans contain a gene encoding the enzyme
phenylalanine hydroxylase
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Converts phenylalanine to tyrosine
Humans with one or two functional copies of
this gene can metabolize phenylalanine
Humans with two copies of a rare inactive
allele cannot metabolize phenylalanine
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Phenylalanine will thus accumulate
It ultimately causes a number of detrimental effects
 Mental retardation, for example
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Phenylketonuria (PKU)
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Newborns are now routinely screened for PKU
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Individuals with the disease are put on a strict
dietary regimen
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Their diet is essentially phenylalanine-free and low
in protein and rich in fruits and vegetables.
These individuals tend to develop normally
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Refer to Figure 1.10
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During Sexual Reproduction, Genes
Are Passed from Parent to Offspring
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Gregor Mendel, in the mid-19th century,
provided the foundation of the science of
genetics
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The principles of inheritance he proposed
can be explained by chromosomes and
their behavior during cell division
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During Sexual Reproduction, Genes
Are Passed from Parent to Offspring
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Sexually-reproducing species are diploid
 Have two copies of each chromosome
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One from each parent
The two copies are termed homologues
 Homologues contain the same genes
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Not necessarily the same alleles
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In humans, most
cells have 46
chromosomes
 23 homologous
pairs
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Note:
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The X and Y
chromosomes of
human males are
not homologous
Figure 1.11
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Gametes
 Sperm and egg cells
are haploid
 Have 23 chromosomes
Figure 1.11
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During Sexual Reproduction, Genes
Are Passed from Parent to Offspring
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The union of sperm and egg during
fertilization restores the diploid number
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Sexual reproduction enhances genetic
variation
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It results in combinations of traits not found in
either parent
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The Genetic Composition of a
Species Evolves Over the Course of
Many Generations
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The genetic makeup of a population can
change over time
 This is termed biological evolution
Biological evolution is possible because of
natural selection
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Natural selection :
 Members of a species compete for essential
resources
 In some individuals, random mutations lead to
beneficial alleles
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Individuals are better adapted to the environment
These individuals are more likely to survive and
reproduce
Therefore, the beneficial alleles are passed on to
subsequent generations
In addition, populations can harbor neutral
mutations (unrelated to survival)
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The Genetic Composition of a
Species Evolves Over the Course of
Many Generations
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Thus, genetic changes can accumulate
These can slowly lead to remarkable
modifications in the characteristics of a
species
 Example:
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The evolution of Equus caballus
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The modern day horse
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Important changes
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Larger size
Fewer toes
Modified jaw
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For grazing
Figure 1.12
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1.2 FIELDS OF GENETICS
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Genetics encompasses four biological disciplines
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Molecular
Cellular
Organismal
Population
It is traditionally divided into three areas
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Transmission genetics
Molecular Genetics
Population Genetics
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Transmission Genetics Explores the
Inheritance Patterns of Traits as They
Are Passed from Parents to Offspring
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Transmission genetics is the oldest field of
genetics
It examines how traits are passed from one
generation to the next
The conceptual framework was provided
by Gregor Mendel in the 1860s
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Genetic determinants pass from parent to
offspring as discrete units
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These are now termed genes
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Transmission Genetics Explores the
Inheritance Patterns of Traits as They
Are Passed from Parents to Offspring
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The basic experimental approach is the
genetic cross
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Two selected individuals are mated
The traits in question are analyzed over
several generations
Analysis is often quantitative in nature
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Molecular Genetics Seeks a
Biochemical Understanding of the
Hereditary Material
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Molecular genetics is the most modern field
of genetics
It deals with the gene itself
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Its features, organization and function
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Molecular Genetics Seeks a
Biochemical Understanding of the
Hereditary Material
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Molecular geneticists study “model organisms”,
such as
 Escherichia coli (a bacterium)
 Saccharomyces cerevisiae (a yeast)
 Drosophila melanogaster (an animal)
 Arabidopsis thaliana (a plant)
The genes found in these organisms behave
similarly as those in humans
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Molecular Genetics Seeks a
Biochemical Understanding of the
Hereditary Material
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Molecular geneticists typically employ the
genetic approach to research
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They study mutant genes that have an
abnormal function
 Example: Loss-of-function mutation
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Population Genetics Is Concerned
With Genetic Variation and Its Role
in Evolution
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Population genetics deals with the genetic
composition of populations and how it
changes over time and space
It connects the work of Mendel on
inheritance to that of Darwin on evolution
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Genetics Is an Experimental Science
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Science allows us to understand our
natural world
Genetics allows us to understand how
genes produce traits
The scientific method underlies scientific
research

It is a standard process that provides ways to
validate (or invalidate) hypotheses about the
natural world
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Genetics Is an Experimental Science
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Finally, remember that science is a social
discipline
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Think of it as a continuous dialogue!
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