Chapter 16 Evolution Of Populations. 16-1 B. Gene Pool I. Genetic variation is studied in...

Chapter 16

Evolution

Of

Populations

16-1

B. Gene Pool

I. Genetic variation is studied in populations

A. A population is a group of individuals of the same species that interbreed

1. All the alleles in a population

a. combined genetic info. of all the members of a population

2. Relative Frequency = How often alleles occur in gene pool (expressed as a percentage)

• Gene Pool for Fur Color in Mice 94

3. Evolution is any change in the relative frequency of alleles in a population.

II. Sources of Genetic Variation

A. Mutations

1. Any change in sequence of DNA

2. result of radiation or chemicals in the environment

3. does not always affect organism’s phenotype

B. Gene Shuffling

1. Responsible for heritable differences due to crossing over

2. Sexual reproduction produces different phenotypes = does not change relative frequency

C. Single-gene and Polygenic traits

1. Phenotypes for a given trait depends on the # of genes controlling the trait

2. Single-gene Traits 3. Polygenic Traits

-controlled by one gene -controlled by many genes

a. only 2 phenotypes possible a. many phenotypes possible

b. examples: Widow’s peak, tongue roll, freckles

b. examples: height, eye color; weight; skin tone

Whether a trait is controlled by a single gene or many genes, can be predicted by examining the frequency of distribution in the population.

16-2

I. Evolution as Genetic Change

A. Natural selection affects which individuals survive and reproduce and which do not.

B. If an individual dies without reproducing = does NOT contribute alleles to gene pool

D. Populations, NOT individual organisms, evolve over time.

C. If an individual produces offspring = the alleles stay in the gene pool

II. Natural Selection on Single Gene Traits

A. Can change relative frequency evolution

B. Example: lizard color mutation caused red and black color: red seen easily = eaten and disappear / black beneficial = increase in numbers

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III. Natural Selection on Polygenic traits

A. can affect the phenotypes in 3 ways1. Directional Selection

a. individuals at one end of the curve have higher fitness

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2. Stabilizing Selection

a. individuals near the center of the curve have higher fitness

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3. Disruptive Selection

a. individuals at both the upper and lower ends of the curve have higher fitness

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IV. Genetic Drift

A. Random change in relative frequency (%)

B. May occur when small group colonizes a new habitat

C. Called Founder effect = migration (examples: Hawaiian fruit flies or English Beetles)

Page 400

English Beetles

Population A

Population B

V. Hardy-Weinberg Principle- p2 + 2pq + q2 = 1

A. Allele frequency will remain constant unless 1 or more factors change

B. No evolution = Genetic Equilibrium

C. 5 conditions to maintain genetic equilibrium

1. Random mating = equal chance to pass alleles

2. Large Population= less genetic drift

3. No migration-No movement of individuals in (immigration) or out (emigration) of population =gene pools kept separate

4. No mutations = no new alleles introduced

5. No natural selection = no phenotypic advantage

16-3

I. Process of Speciation

A. Isolating Mechanisms lead to Speciation

2. Behavioral isolation= Differences in courtship or other behaviors (page 404)

1. Reproductive isolation = new species cannot interbreed

(formation of new species)

3. Geographic isolation = Separated by barriers (rivers/mountain) (page 405)

4. Temporal isolation =

2 or more species reproduce at different times (different seasons/ different times of day)

B. Speciation of Galapagos Finches (Page 409)

1. Founders arrive – finches from S.A. to Galapagos

2. Geographic Isolation– part of group A goes to another island

3. Changes in Gene Pool – population adapt to environment = changes

4. Reproductive Isolation – pop. B goes back to first island A and B cannot interbreed.5. Ecological Competition – A and B compete for available seeds in same habitat; continue to evolve = species C

6. Continued Evolution – repeated over and over again

16-1

Which of the following statements is TRUE? A. The relative frequency of an allele is not related

to whether the allele is dominant or recessive.B. Mutations always affect an organism's

phenotype.C. Crossing-over decreases the number of different

genotypes that appear in an offspring.D. Evolution does not affect the frequency of

genes in a gene pool.

16-1

Most inheritable differences are a result of

A. gene shuffling during the production of gametes.

B. frequency of alleles.

C. mutations.

D. DNA replication.

16-1

The main sources of inherited variation are

A. gene shuffling and mutations.

B. gene pools and frequencies.

C. single-gene and polygenic traits.

D. genotypes and phenotypes.

16-1

A widow's peak in humans is an example of a(an)

A. invariable trait.

B. single-gene trait.

C. polygenic trait.

D. mutation.

16-1

A graph of the length of the little finger on the left hand versus the number of people having fingers of a particular length is a bell-shaped curve. This indicates that finger length is a

A. single-gene trait.

B. polygenic trait.

C. randomly inherited trait.

D. strongly selected trait.

16-2

Which of the following patterns of natural selection on polygenic traits favors both extremes of a bell curve?

A. stabilizing selection

B. disruptive selection

C. directional selection

D. genetic drift

16-2

Which of the following events could lead to genetic drift?A. A few new individuals move into a large, diverse

population.B. A few individuals from a large, diverse population

leave and establish a new population.C. Two large populations come back together after a few

years of separation.D. The mutation rate in a large population increases due

to pollution.

16-2

The situation in which allele frequencies remain constant in a population is known as

A. genetic drift.

B. the founder effect.

C. genetic equilibrium.

D. natural selection.

16-2

Which of the following conditions is required to maintain genetic equilibrium in a population?

A. movement in or out of the population

B. random mating

C. natural selection

D. small population

16-2

According to the Hardy-Weinberg principle, no evolution will take place ifA.all five of the Hardy-Weinberg conditions are met.B. any one of the Hardy-Weinberg conditions is met.C. at least three of the Hardy-Weinberg conditions are

met.D. none of the Hardy-Weinberg conditions are met.

16-3

When two species do not reproduce because of differences in mating rituals, the situation is referred to as

A. temporal isolation.

B. geographic isolation.

C. behavioral isolation.

D. reproductive isolation.

16-3

The most important factor involved in the evolution of the Kaibab and Abert squirrels of the American Southwest appears to be




D. different food sources.

16-3

One finding of the Grants' research on generations of Galápagos finches was that

A. natural selection did not occur in the finch

B. natural selection can take place often and very rapidly.

C. beak size had no effect on survival rate of the finches.

D. natural selection was slow and permanent.

16-3

All of the following played a role in speciation of Galápagos finches EXCEPT

A. no changes in the gene pool.

B. separation of populations.

C. reproductive isolation.


16-3

Beak size in the various groups of Galápagos finches changed primarily in response to

A. climate.

B. mating preference.

C. food source.

D. availability of water.