Bio132: 21.2 Evolution of Population 2

A _____ is a localized group of individuals capable of interbreeding and producing fertile offspring

Population

A _____ consists of all the alleles for all loci in a population

Gene pool

An allele for a particular locus is ____ if all individuals in a population are ______for the same _____

Fixed, homozygous, allele

What happens to allele and genotype frequencies if no evolution occurs?

They remain constant.

What are the assumptions of Hardy-Weinberg equilibrium?

• No natural selection

• Random mating

• No genetic drift (very large population)

• No gene flow

• No mutation

What is the Hardy–Weinberg equation?

p^2+2pq+q^2=1

Where:

• p = frequency of one allele

• q = frequency of the other allele

• p+q=1

Which mechanisms can alter allele frequencies in a population?

Natural selection, genetic drift, and gene flow.

What results in certain alleles being passed to the next generation in greater proportions?

Differential success in reproduction

What happened to alleles that conferred resistance to DDT after DDT was widely used?

The resistance allele increased in frequency after DDT was widely used in agriculture.

The ____ a sample, the _____ likely it is that chance alone will cause deviation from a predicted result

Smaller, more

_____describes how allele frequencies fluctuate unpredictably from one generation to the next

Genetic drift

Genetic drift tends to_____through losses of alleles, especially in small populations

Reduce genetic variation

What is the founder effect?

The founder effect occurs when a few individuals become isolated from a larger population and establish a new population with a different allele frequency.

Allele frequencies in the small founder population can be ____ from those in the larger parent population due to _____

Different, chance

What is the bottleneck effect?

The bottleneck effect occurs when a population’s size is drastically reduced due to a sudden environmental change, leading to a loss of genetic variation.

How can genetic drift affect a population’s gene pool after a bottleneck or founder event?

By chance, the resulting gene pool may no longer reflect the original population’s gene pool.

In a bottleneck event example using marbles, what can happen by chance in the surviving population?

By chance, blue marbles may be overrepresented in the surviving population.

What is an example of a real species affected by a bottleneck event?

The Florida panther (Puma concolor coryi).

How does chance play a role in evolution by natural selection?

New genetic variations arise by chance through mutation.

What does “sorting” mean in natural selection?

Beneficial alleles are sorted and favored because individuals with them are more likely to survive and reproduce.

Which mechanism consistently results in adaptive evolution?

Only natural selection, because it increases the frequency of alleles that improve fitness.

_____ is the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals

Relative fitness

Selection indirectly _____ certain _____ by acting directly on phenotypes

Favors, genotypes

_____ selection favors individuals at one end of the phenotypic range

Directional

_____ selection favors individuals at both extremes of the phenotypic range

Disruptive

_____ selection favors intermediate variants and acts against extreme phenotypes

Stabilizing

How do striking adaptations arise?

They arise by natural selection.

What is an example of an adaptation in octopuses?

Some octopuses can rapidly change color for camouflage.

What is an example of an adaptation in snakes?

Their jaws allow them to swallow prey larger than their heads.

Natural selection increases the frequencies of ____ that enhance _____

Alleles, survival and reproduction

Adaptive evolution occurs as the match between an _____ and its ______ increases

Organism, environment

Because the environment can change, adaptive evolution is a _______, ______ process

Continuous, dynamic

Genetic drift and gene flow ______ consistently lead to adaptive evolution, as they can increase or decrease the match between an organism and its environment

Do not

______ selection is natural selection for mating success

Sexual

What can sexual selection result in?

Sexual dimorphism — marked differences between the sexes in secondary sexual characteristics.

How can male showiness due to mate choice affect survival?

It can increase a male’s chances of attracting a female while decreasing his chances of survival.

What is intrasexual selection?

Intrasexual (within-sex) selection is competition among individuals of one sex, often males, for mates of the opposite sex.

What is intersexual selection?

Intersexual (between-sexes) selection, or mate choice, occurs when individuals of one sex (usually females) are selective in choosing their mates.

How do female preferences evolve according to the “good genes” hypothesis?

If a male trait signals genetic quality or health, females that prefer that trait produce healthier offspring.

What happens over time under the “good genes” hypothesis?

Both the advantageous male trait and the female preference for that trait increase in frequency.

_____ maintains genetic variation in the form of _____ recessive alleles

Diploidy, hidden

Why can recessive alleles persist in a population?

Because heterozygotes can carry recessive alleles that are hidden from the effects of selection.

What happens during balancing selection?

Natural selection maintains two or more phenotypic forms in a population by keeping multiple alleles at stable frequencies.

What mechanisms are included in balancing selection?

• Heterozygote advantage

• Frequency-dependent selection

______occurs when heterozygotes have a higher fitness than do both homozygotes

Heterozygote advantage

Natural selection will tend to______ at that locus

Maintain two or more alleles

What is an example of balancing selection in humans?

The sickle cell allele: it can cause harmful hemoglobin mutations but also provides resistance to malaria.

What is frequency-dependent selection?

It occurs when the fitness of a phenotype declines if it becomes too common in the population.

How does frequency-dependent selection favor phenotypes?

Selection favors whichever phenotype is less common in a population.

What is an example of frequency-dependent selection?

Scale-eating fish: selection maintains roughly equal numbers of “right-mouthed” and “left-mouthed” individuals.

Selection can act only on _____

Existing variations

Evolution is limited by _____

Historical constraints

Adaptations are often _____

Compromises

Chance, natural selection, and the environment _____

Interact