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Chapter Three: Evolutionary
Genetics
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Evolutionary Genetics
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What are genes, and how do they
produce the traits that make a pea plant
or a human being?
What do we know about the nature of the
human genome?
What are the basic laws of inheritance?
What processes bring about the variation
we see among members of a species and
between parents and offspring?
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Evolutionary Genetics

How Genes Work

The gene is that portion of the DNA
molecule that carries the codon
sequence for a particular protein.
Feature
base
codon
gene
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Analogue
letter
word
sentence
Meaning
amino acid
protein
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Fig 3.2
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definitions

Particulate


The idea that biological traits are controlled by individual
factors rather than by a single all-encompassing hereditary
agent.
Genes

Those portions of the DNA molecule that code for a
functional product, usually a protein.
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definitions

Proteins
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Molecules that make cells and carry out cellular functions.
Amino Acids

The chief components of proteins.
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definitions

Enzymes

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Chromosomes
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Strands of DNA in the nucleus of a cell.
Deoxyribonucleic Acid (DNA)

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Proteins that control chemical processes.
The molecule that carries the genetic code.
Nucleotide

The basic building block of DNA and RNA, made up of
a sugar, a phosphate, and one of four bases.
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definitions

Replication


The copying of the genetic code
during cell division.
Codon

The three-base sequence that codes
for a specific amino acid. Technically,
the sequence on the mRNA.
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definitions

Protein Synthesis


The process by which the genetic
code puts together proteins in the cell.
Messenger Ribonucleic Acid
(mRNA)

The molecule that carries the genetic
code out of the nucleus for translation
into proteins.
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definitions

Transcription

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The process during which messenger
RNA is formed from the DNA code.
Translation

The process during which the mRNA
code builds a protein using amino
acids supplied by tRNA.
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definitions

Transfer Ribonucleic Acid
(tRNA)
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Polygenic
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RNA that lines up amino acids along mRNA
to make proteins.
a trait coded for by more than one gene.
Monogenic

A trait coded for by a single gene.
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Evolutionary Genetics

An Overview of the Human Genome
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
As of spring 2003, nearly the entire
human genome has been sequenced.
We now have a baseline from which
scientists will be able to further
research the genome and compare
other people and populations.
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Evolutionary Genetics

From Gene to Trait
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Combinations of alleles give us
genotypes.
These genotypes produce a trait.
The observable trait is the phenotype.
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Fig 3.5
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definitions
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Genome
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Mendelian Genetics
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The basic laws of inheritance discovered by Gregor
Mendel in the nineteenth century.
Alleles
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The total genetic endowment of an organism.
Variants of a gene.
Genotype

The alleles possessed by an organism.
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definitions

Homozygous
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Having two of the same allele in a
gene pair.
Heterozygous

Having two different alleles in a gene
pair.
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definitions
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Phenotype
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The chemical or physical results of the
genetic code.
Dominant

The allele of a heterozygous pair that
is expressed in the phenotype.
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definitions
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Recessive
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Codominant
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When both alleles of a pair are expressed in the phenotype.
Environmental
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The allele of a pair that is only expressed if homozygous.
Here, any nongenetic influence on the phenotype.
Mutation

Any mistake in an organism’s genetic code.
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Evolutionary Genetics
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How Inheritance Works

The variation between parents and
offspring is the result of the processes
of segregation and fertilization, and
variation is the raw material of
evolution.
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Fig 3.7
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definitions
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Mitosis

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The process of cell division that
results in two exact copies of the
original cell.
Gametes

The cells of sexual reproduction,
which contain only half the
chromosomes of a normal cell.
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definitions

Zygote
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Segregation
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The fertilized egg before cell division begins.
In genetics, the breaking up of allele pairs in
the production of gametes.
Meiosis
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The process of cell division in which
gametes are produced.
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definitions
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Independent Assortment
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Linkage
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When genes occur on the same chromosome and are
inherited together.
Crossing Over
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When genes on different chromosomes segregate to
gametes independently of one another.
When sections of chromosomes switch between
chromosome pairs during meiosis.
Recombination

The exchange of genetic material between pairs of
chromosomes during meiosis.
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Evolutionary Genetics

Summary
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Evolutionary change is at its most
basic level genetic change.
Segregation, independent assortment,
crossing over, and mutation produces
new genetic variation.
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Questions for further thought
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New information about the specific nature of the
human genome indicates, among other things,
that we are, from several perspectives, not all
that different from other organisms.
We have far fewer genes that would be expected
given our complexity. We share a great many of
those genes with other organisms, from mice to
bacteria.
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What philosophical issues might follow from these
facts?
How might these facts be practically applied?
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Questions for further thought
We’ve considered some of the ethical concerns regarding
cloning.

How do you feel about the goals of reproductive cloning?
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Are they all equally worthwhile?
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What constraints should be placed on cloning? Should
any reproductive cloning on humans be allowed?
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What about stem cell research?
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Do the same issues apply?
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Should companies be allowed to “own” certain lines of
stem cells that came from a human and would be used to
improve the health of other humans?
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