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Genetics: Analysis and Principles
Robert J. Brooker
CHAPTER 1
OVERVIEW OF
GENETICS
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INTRODUCTION
• Human Genome Project?
– Formally launched in 1990
– Aimed to decode our GENOME-all of the
DNA found within all of our chromosomes
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INTRODUCTION
• A “working draft” of the human genome
sequence was completed in 2000
– Nearly 3 billion nucleotides
– 25000 of genes
• The study of the human genome provides
fundamental molecular details
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INTRODUCTION
• 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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Figure 1.1a
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INTRODUCTION
• While trying to understand genes and their
function, scientists have developed many
genetic technologies
– DNA fingerprinting
– Mammalian cloning
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INTRODUCTION
• DNA fingerprinting
– Now a common tool of forensic science
• Mammalian cloning
– In 1997, Ian Wilmut and colleagues cloned the
first mammal, A sheep named Dolly (Figure 1.2)
• Cows, mice, goats, pigs and cats have now been
cloned
– Fears that the technology may be applied to
humans led to legislative bans on human cloning
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What about in our country?
• Oyalı- First Turkish clonned baby lamb
• 21 November 2007 First clonned sheep “Oyalı”
• 30 March 2011 “Bahar” The lamb of Oyalı
Human ?
Hwang Woo-suk Seoul National
University
He announced that he has generated embriyonic stem cells via the
embryonic clonning.
INTRODUCTION
• Genetic technologies allow the
modification of animals in various ways
• For example, mice can be made to glow
green (Figure 1.3)
– A jellyfish gene encoding a green fluorescent
protein is introduced into lab mice
– Upon exposure to ultraviolet light, the mice
emit a bright green color
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1.1 THE RELATIONSHIP
BETWEEN GENES AND TRAITS
• Genetics is the study of heredity and variation
– It is the unifying discipline in biology
• The central theme in genetics is the gene
– The gene is classically defined as a ‘unit’ of heredity
– The modern definition is a segment of DNA that
produces a functional product such as a polypeptide.
– Genes provide traits of an organism
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Figure 1.4
Nucleotide building blocks
are used to make long
strands of DNA which
associate with proteins
and form chromosomes.
The chromosomes are
contained within the nucleus.
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Each Cell Contains Many Different
Proteins That Determine Cellular
Structure And Function
• The characteristics of a cell largely depend
on the proteins it produces
• Proteins have diverse biological functions
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• Structural proteins
– Tubulin
• Aggregates to form microtubules
• Plays role in cell shape and movement
• Contractile proteins
– Myosin
• Plays role in muscle contraction
• Hormonal proteins
– Insulin
• Regulates the level of glucose in the blood
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• A particularly important group of proteins
are the enzymes
– Enzymes are biological catalysts
– Catabolic enzymes
• Involved in the breakdown of large molecules into
smaller ones
• Provide energy for the activities of the cell
– Anabolic enzymes
• 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
• The genetic material in most 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
• DNA is a polymer of nucleotides
– Each nucleotide contains one nitrogenous base
•
•
•
•
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
• For example:
• 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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• The DNA in living
cells is contained
within large structures
termed chromosomes
• Human cells have a
total of 46
chromosomes
• Each chromosome is
a complex of DNA
and proteins
• An average human
chromosome contains
– More than a 100
million nucleotides
– about 1,000 different
genes
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The Information Within the DNA Is
Accessed During the Process of
Gene Expression
• Gene expression occurs in two steps
– Transcription
• The genetic information in DNA is copied
into a nucleotide sequence of ribonucleic
acid (RNA)
– Translation
• 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
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The Molecular Expression of Genes
Within Cells Leads to an Organism’s
Outwardly Visible Traits
• A trait is any characteristic that an organism displays
• We usually focus on Morphological traits
– Affect the appearance of the organism
– Example: The color of a flower
• There are also Physiological traits
– Affect the function of the organism
– Example: Ability to metabolize a sugar
• We can even identify Behavioral traits
– Affect the ways an organism responds to the
environment
– Example: Mating calls of bird species
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Inherited Differences in Traits Are
Due to Genetic Variation
• Genetic variation refers to differences in inherited
traits among individuals within a population
– For example: In petunias, white vs. purple flowers
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• Genetic variation is a result of various types of
changes at the molecular level
– 1. Gene mutations
• Small differences in gene sequences
• Lead to two or more expression forms or alleles of
the same gene
– 2. Changes in chromosome structure
• Large segments of the chromosome may be lost or
duplicated
– 3. Changes in chromosome number
• Single chromosomes may be lost or gained
– Refer to Figure 1.9a
• A whole set of chromosomes may be inherited
– Refer to Figure 1.9b
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Wheat with 6n (3x2n) chr.
Down Syndrome with 47 chr.
Traits Are Governed by Genes and
by the Environment
• 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
– For example, an individual’s diet has an effect
on his/her height and weight and even
intelligence
• In some cases, the environment dictates
whether a disease is manifested in an
individual or not
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• Phenylketonuria (PKU)
– Humans contain a gene encoding the enzyme
phenylalanine hydroxylase
• 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
• Phenylalanine will thus accumulate
• It ultimately causes a number of detrimental effects
– Mental retardation, for example
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Same but different
Chris, left, and Xand van Tulleken have identical DNA but differing pain
responses due to their life experiences
Read more: http://www.dailymail.co.uk/health/article-1216253/Theyre-identical-twins--age-10-years-other.html#ixzz2fPzhq1V8
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During Sexual Reproduction, Genes
Are Passed from Parent to Offspring
• Gregor Mendel, in the mid-19th century,
provided the foundation of the science of
genetics
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During Sexual Reproduction, Genes
Are Passed from Parent to Offspring
• Sexually-reproducing species are diploid
– Have two copies of each chromosome
• One from each parent
– The two copies are termed homologues
– Homologues contain the same genes
• Not necessarily the same alleles
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• In humans, most
cells have 46
chromosomes
– 23 homologous
pairs

Note:

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
• The union of sperm and egg during
fertilization restores the diploid number
• Sexual reproduction enhances genetic
variation
– It results in combinations of traits not found in
either parent
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1.2 FIELDS OF GENETICS
• Genetics encompasses four biological disciplines
–
–
–
–
Molecular
Cellular
Organismal
Population
• It is traditionally divided into three areas
– 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
• 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
– Genetic determinants pass from parent to
offspring as discrete units
• 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
• The basic experimental approach is the
genetic cross
– Two selected individuals are mated
– The traits in question are analyzed over
several generations
– Analysis is often quantitative in nature
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Transmission Genetics Explores the
Inheritance Patterns of Traits as They Are
Passed from Parents to Offspring
• Transmission genetics is covered in Chapters 2-8
– Chapter 2
• Mendelian patterns of inheritance
– Chapter 3
• Chromosomes and their roles in inheritance
– Chapters 4-8
• Complexities in transmission genetics
– Linkage
– Non-Mendelian patterns of inheritance
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Molecular Genetics Seeks a Biochemical
Understanding of the Hereditary Material
• Molecular genetics is the most modern field
of genetics
• It deals with the molecular features of DNA
and how these underlie gene expression
– A genes features, organization and function
– Detailed analysis of DNA, RNA and proteins
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Molecular Genetics Seeks a Biochemical
Understanding of the Hereditary Material
• 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
• Molecular geneticists typically employ the
genetic approach to research
– They study mutant genes that have an
abnormal function
• Example: Loss-of-function mutation
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• Molecular genetics is covered in Chapters 9-23
– Chapters 9-15
• Structure, replication, expression and regulation of the
genetic material
– Chapters 16 and 17
• Mutations and rearrangements of the genetic material
– Chapters 18-21
• Recombinant DNA technology and computer-based
approaches to studying the genetic material
– Chapter 22
• Role of the genetic material in human diseases
– Chapter 23
• Role of the genetic material in development
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Population Genetics Is Concerned With
Genetic Variation and Its Role in
Evolution
• 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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Population Genetics Is Concerned With
Genetic Variation and Its Role in
Evolution
• Population genetics is covered in Chapters 24-26
– Chapter 24
• The role of the environment and genetics in the
expression of traits
– Chapter 25
• How and why some alleles are maintained in populations
– Chapter 26
• The genetics behind the process of evolution
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