Download Single-Gene and Polygenic Traits

Chapter 17 Evolution of Populations
Goal: to understand how populations evolve to form new species
17.1 Genes and Variation
Genetics Joins Evolutionary Theory
Genotype and Phenotype in Evolution

Organisms have two set of genes, one from the mother and one
from the father. Specific forms of a gene are called
_____________.

A person’s __________ is referring to their particular combination
of alleles.

A person’s genotype along with the environmental conditions
refers to the ____________ (eye color, height, hair color, etc.).

Natural selection works on the individual’s ____________ not the
___________________. Nature will select _________________
not ______________.

Nature will _____________ which ______________ is better
suited for the environment and as a result more copies of their
___________ will be passed on since they have better
__________________.
Population and Gene Pools

A ___________________ refers to a group of individuals that are
of the same species and produce offspring.

Members of the same population share a common set of genes
and this is known as the ___________ ___________.

The ___________ _____________ refers to the number of times
an allele occurs in a gene pool compared to the total number of
alleles in that pool for the same gene.
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18 white
9 red

If the allele frequency changes then the
population is _______________. Individuals
may evolve but changes in the _____________ frequency show up in a
__________________.
Question: Calculate the total number of alleles.
Question: What is the allele frequency of each allele? Your answer
should be in a percentage.
Sources of Genetic Variation
Mutations

Mutations either involve individual ___________or larger pieces
of ____________________. Some mutations are
______________since they don’t change the organisms
phenotype

Mutations that matter to evolution occur in _______ _________
cells (sperm and egg) since they can be passed on from generation
to generation. Mutations that occur in skin cells ____________ be
passed on to the next generation.
Genetic Recombination in Sexual Reproduction

___________________ assortment and _______________ over
during meiosis provide inheritable variation. These two processes
increase the number of _________________ created in each
generation.
Lateral Gene Transfer

Simple forms of life, like bacteria, can increase ____________
variation by simply picking up genes from other organisms
through the process called ____________ _________
____________.
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Single-Gene and Polygenic Traits
Single – Gene Traits

The number of phenotypes produced for a certain trait depends
on how many genes control the trait.

If there are two or three distinct phenotypes, than a single gene
may be responsible and this is known as a _________ ________
trait.
A widow’s peak is an example of a single gene trait. There is one
gene with two alleles for this trait, one allele for the trait (W) and
one for not having the trait (w). Complete the Punnet Square you
can determine the frequency of the phenotypes. If you are not
familiar with Punnet Squares refer to page 316 of Biology Miller &
Levine
W
w
W
w
Question: What is the frequency for having the widow’s peak?
________
Question: What is the frequency for not having the widow’s peak?
________
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Polygenetic Traits

When traits are controlled by two or more genes they are
considered _______________ traits. Each gene often has two or
more _____________

An example of polygenic traits would be human blood types. This
polygenic trait is controlled by three alleles, A, B and O. Allele A
and B are dominant to allele O which is recessive. There are four
blood types; A, B, AB and O.
17.2 Evolution as Genetic Change in Populations
How Natural Selection Works
Natural Selection on Single – Gene Traits

Evolution is any change, over time, of the ___________ frequency
in a population.

Natural selection on single-gene traits can lead to changes in
allele frequencies and will then lead to changes in
____________________ frequencies.

If there is no pressure from natural selection, then there will be
no change in fitness. If there is selective pressure then there will a
change in fitness
Question: The diagram shows bacteria before and after exposure
to antibiotics. What is the selective pressure?
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Natural Selection on Polygenetic Traits

Natural selection on polygenic traits results in three types of
selection: ___________ selection, __________ selection and
_____________ selection.

Directional selection occurs when individuals at one end of the
bell curve have ________ ___________ than those at the middle
or other end of the curve.
Use the graph below to show directional selection.

Stabilizing selection occurs when individuals near the
_____________ of the bell curve have higher fitness then those at
either end.
Use the graph below to show stabalizing selection.
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
Disruptive selection occurs when individuals on the _________
______________ of the bell curve have higher fitness that those
near the middle of the curve.
Use the graph below to show disruptive selection.
Genetic Drift

The random change in allele frequency is called __________
____________.
Genetic Bottlenecks

When a small populations allele frequency dramatically reduces
due to some natural disaster or disease this is known as
the____________ __________ effect.
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Founder Effect

When an allele frequency changes as a result of migration of a
small subgroup of a population, this is known as the
_____________ ____________. The founding individuals may
carry different allele frequencies than the _________ population.
Evolution Versus Genetic Equilibrium

When there is no change in the allele frequencies, the population
is not evolving and this is known as ___________ _____________.
Sexual Reproduction and Allele Frequency

Sexual reproduction ________ _______ change the allele
frequencies in a population. Hypothetically, sexually reproducing
organisms could remain in _________ ____________.
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The Hardy-Weinberg Principle

The Hardy Weinberg principle states that the allele frequency
should stay ___________ unless one or more factors cause the
frequency to change. The Hardy Weinberg priciple will make
predictions about __________ frequency in a ___________ using
the following formula.
P2 + 2pq + q2 = 1
P+q=1
In words:
(frequency of AA) + (frequency of Aa) + (frequency of aa) = 100%
And
(frequency of A) = (frequency of a) = 100%
Question: Suppose that in one generation the frequency for the
allele B is 56% (p= 0.56)and the frequency of allele b is 44% (q=.44).
If this population is at genetic equilibrium then we can predict
what the percentage of each genotype for the next generation.
Calculate.
(BB)
P2 =
(bb)
q2 =
(Bb)
2pq =
If the population above does not show these predicted
phenotype frequencies, _______________ is taking place

The Hardy Weinberg principle predicts five conditions that would
disrupt the genetic equilibrium and cause evolution to occur:
Due to _____________ selection, mates are chosen due to
size, coloration, strength, etc. and do not mate
____________. This works against _______________.
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Genetic drift can occur in ___________ populations and
cause evolutionary change
_________ _________ occurs when individuals moving in
or out of a population disrupt the genetic equilibrium.
_______________ in genes can disrupt allele frequencies
causing ________________ to occur.
Nature will select certain genotypes according to their
fitness and these will ________________ genetic
equilibrium and evolution will occur.
17.3 The Process of Speciation
Isolating Mechanisms

A ____________ is a population or group of populations that can
interbreed and produce fertile off spring.

________________ refers to the formation of a new species.

________________ ________________ occurs when some
members no longer interbreed with members of the population.
As a result of reproductive isolation the separated members can
evolve into new _________________.
Question: Use this diagram below to explain how this is an
example of reproductive isolation
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Reproductive isolation can develop a variety of ways:
________________ Isolation

When groups develop _____________ in courtship rituals or
other behaviours
_______________ Isolation

Geographic barriers (rivers, canyons,
mountains)_____________ two populations
______________ Isolation

When two or more populations start to __________ at
different times
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Read pages 496 and 497 and explain how natural selection and
behavioural isolation may have led to reproductive isolation in
Darwin’s Finches
Founder Arrive:
Geographic Isolation:
Changes in Gene Pool:
Behavioral Isolation:
Competition and Continued Evolution:
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