Chapter 23

The Evolution of Populations

Key Concepts

1. Genetic variation makes evolution possible

2. The Hardy-Weinberg equation can be used to test whether a population is evolving.

3. Natural selection, genetic drift, and gene flow can alter frequencies in a population.

4. Natural selection is the ONLY mechanism that consistently causes ADAPTIVE evolution.

Framework

POPULATIONS

consists of individuals that show

geneticvariation

is substrate for

natural selection

mechanism of

adaptive evolution

are units that undergo

Evolution

change in

allele frequencies

may change due to

natural selection,genetic drift, gene flow

estimated by

p + q=1 (alleles)P2 + 2pq + q2=1 (genotypes)

may be in

Hardy-Weinbergequilibrium

equation is

large population,

no gene flow,

no mutations,

random mating,

no natural selection

1. How does natural selection act on individuals?

True/False Individual organisms evolve.

Each individual organism’s trait affects its survival and reproductive success compared with other individuals.

2. What is microevolution?

Change in allele frequencies in a population over generations.

3. What are the three main causes of microevolution?

1. Natural selection 2. genetic drift (chance events)

3. gene flow (transfer of alleles between populations)

Genetic variation makes evolution possible

Natural selection is the mechanism for evolution.

Individuals differ in their inherited traits and selection acts on the differences

4. What are the sources of genetic variation?

Mutation and sexual reproduction

5. What is genetic variation?

Differences among individuals in the composition of their genes or other DNA segments.

6. Phenotype is the product of ____________ and _______________. GENOTYPE THE ENVIRONMENT

Nemoria arizonaria

Raised on a diet of oak flowers resemble the flowers

Raised on a diet of oak leaves resemble twigs

EC: Is there a difference in phenotype in the adult moth?

TRUE/FALSE Without genetic variation, evolution cannot occur.

TRUE!!!!!!Genetic variation provides the raw material for evolutionary change

7. Characters that vary in a population may be ____________ or ____________DISCRETE QUANTITATIVE

Discrete characters: either-or basis

8. Discrete characteristics are determined by ________________________________single gene locus with different alleles

9. Quantitative characters usually results from the ________________________ __________________________.

influence of two or moregenes on single phenotype

Variation in quantitative characters involve a continuum.

Hair color

Eye color

Skin color

Guess this genotype.

AABBCC

You will NOT need to know AVERAGE HETEROZYGOSITY

A way to measure variation within a population

10. What is geographic variation? Differences in the genetic composition of separate populations.

The Kaibab was separated by the Colorado River.

The Kaibab squirrel evolved from the Abert squirrel.

The source of variation here is the pattern of fused chromosomes.

Variation here is a result of chance events (genetic drift).

Sources of genetic variation

MutationGene duplicationProcess that produce new alleles and new genesSexual reproduction

http://goose.ycp.edu/~kkleiner/ecology/EvolEcologyimages.htm