Ch 23 - The Evolution of Populations

What are the 3 modes of selection?

1. Directional 2. Disruptive 3. Stabilizing

What 2 ways can genetic variation be measured by?

1. Gene variability 2. Nucleotide variability

What 3 major factors alter allele frequencies and bring about most evolutionary change?

1. Natural selection 2. Genetic drift 3. Gene flow

What mechanisms cause allele frequency change?

1. Natural selection 2. Genetic drift 3. Gene flow

What are the 5 conditions for Hardy-Weinberg equilibrium?

1. No mutations 2. Random mating 3. No natural selection 4. Extremely large population size 5. No gene flow

What is microevolution?

A change in allele frequencies in a population over generations

What is mutation?

A change in the nucleotide sequence of DNA

What is sexual selection?

A process in which individuals with certain inherited characteristics are more likely to acquire mates than other individuals of the same sex

What is adaptive evolution?

A process in which traits that enhance survival or reproduction increase in frequency over time

What kind of evolution can natural selection cause?

Adaptive evolution

What is a gene pool?

All the alleles from all loci in a population

How is nucleotide variability measured?

By comparing DNA sequences of 2 or more individuals

How can new genes and alleles arise?

By mutation or gene duplication

How can sexual reproduction result in gene variation?

By recombining existing alleles

What can gene flow do to the fitness of a population?

Can increase fitness

What is gene flow?

Consists of the movement of alleles among populations

What is intrasexual selection?

Direct competition among individuals of one sex (often males) for mates of the opposite sex

What is the founder effect?

Example of genetic drift Occurs when a few individuals become isolated from a larger population

What is the bottleneck effect?

Example of genetic drift Occurs when there is a drastic reduction in population size due to a sudden change in the environment

What is disruptive selection?

Favors individuals at both extremes of the phenotypic range

What is directional selection?

Favors individuals at one extreme end of the phenotypic range

What is stabilizing selection?

Favors intermediate variants and acts against extreme phenotypes

What are mutation rates like in viruses?

High mutation rates and short generation times

What does genetic drift describe?

How allele frequencies fluctuate unpredictably from one generation to the next

Are mutation rates high or low in animals and plants?

Low (About 1 mutation in every 100,000 genes per generation)

What are mutation rates like in prokaryotes?

Low mutation rates, but short generation times allow mutations to accumulate rapidly

What is sexual dimorphism?

Marked differences between the sexes in secondary sexual characteristics

What is heterozygote advantage?

Occurs when heterozygotes have a higher fitness than both homozygotes

What is balancing selection?

Occurs when natural selection maintains stable frequencies of 2 or more phenotypic forms in a population

What is intersexual selection?

Often called "mate choice" Occurs when individuals of one sex (usually females) are choosy in selecting their mates

Who evolves: individuals or populations?

Populations

What kinds of populations are in Hardy-Weinberg equilibrium?

Populations where gametes contribute to the next generation randomly and Mendelian inheritance occurs

What does gene flow do to variation in populations?

Tends to reduce variation over time

What does average heterozygosity measure?

The average percent of loci that are heterozygous in a population Provides the measure of genetic variation for a population

What is relative fitness?

The contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals

What is frequency-dependent selection?

The fitness of a phenotype depends on how common it is in a population

What does the Hardy-Weinberg equation describe?

The genetic makeup we expect for a population that is not evolving at a particular locus

What does it mean if the observed genetic makeup of a population differs from expectations under Hardy-Weinberg?

The population may be evolving

What is a prerequisite for evolution by natural selection?

Variation in heritable traits

What are neutral variations?

Variations that result in no selective advantage or disadvantage

Which of the following is most likely to cause a phenotypic effect? a) a two-base-pair deletion in a coding region b) a base-pair substitution in an intron c) a protein translated incorrectly from an mRNA d) a ten-base-pair duplication in a promoter e) All are equally likely to cause a phenotypic effect.

a) a two-base-pair deletion in a coding region

In evolutionary terms, an organism's fitness is measured by its _____. a) stability in the face of environmental change b) contribution to the gene pool of the next generation c) genetic variability d) mutation rate e) health

b) Contribution to the gene pool of the next generation

Which of the following is required in order for evolution to occur? a) a large population b) heritable variation c) nonrandom, differential reproductive success d) a long time e) all of the above

b) Heritable variation

Red short-horned cattle are homozygous for the red allele, white cattle are homozygous for the white allele, and roan cattle are heterozygotes. Population A consists of 36% red, 16% white, and 48% roan cattle. What are the allele frequencies? a) red = 0.36, white = 0.16 b) red = 0.6, white = 0.4 c) red = 0.5, white = 0.5 d) Allele frequencies cannot be determined unless the population is in equilibrium.

b) red = 0.6, white = 0.4

Which of the following is not an example of heritable genetic variation? a) a two-base-pair deletion in a coding region b) a base-pair substitution in an intron c) a protein translated incorrectly from an mRNA d) a ten-base-pair duplication in a promoter e) All are examples of heritable genetic variation.

c) A protein translated incorrectly from an mRNA

Indicate which of the Hardy-Weinberg conditions is being violated in this example: Due to global warming, a river has dried up, allowing two different rabbit populations that were previously isolated to mate with one another. a) large population size b) no mutation c) no gene flow d) random mating occurring e) no selection

c) No gene flow

What is the ultimate source of new heritable variation in populations? a) sexual reproduction (e.g., independent assortment, recombination, random mating) b) gene flow (e.g., immigration/emigration) c) selection (e.g., for favorable traits, against deleterious traits) d) mutation (e.g., new alleles from errors in replication/ recombination) e) all of the above

d) Mutation (e.g., new alleles from errors in replication/recombination)

Indicate which of the Hardy-Weinberg conditions is being violated in this example: Male elephant seals show aggression toward other males, resulting in dominant males mating with several females and other males mating with few or no females. a) large population size b) no mutation c) no gene flow d) random mating occurring e) no selection

d) Random mating occurring

Indicate which of the Hardy-Weinberg conditions is being violated in this example: Some moths on a tree are easier to see due to their lighter color and therefore are eaten by predators more often. a) large population size b) no mutation c) no gene flow d) random mating occurring e) no selection

e) No selection

What does p (or q) and p^2 (or q^2) represent in the Hardy-Weinberg equation?

p (or q) = allele frequency p^2 (or q^2) = gene frequency