Hardy-Weinberg

Question 1

Hardy Weinberg equilibrium

Answer 1

a model in which allele frequencies do not change across generations, and genotype frequencies can be predicted from allele frequencies.

Question 2

allele frequencies

Answer 2

measure the amount of genetic variation

Question 3

calculations of allele and genotype frequencies in a population

Answer 3

allow biologists to measure evolutionary change

Question 4

gene pool

Answer 4

sum of all copies of all alleles at all loci in a population.

the sum of the genetic variation in the population

Question 5

allele frequency

Answer 5

Proportion of an allele in the gene pool.

p=number of copies of the allele in the population/total number of copies of all alleles in the population

Question 6

genotype frequency

Answer 6

Proportion of each genotype in the population.

Question 7

Do populations in nature ever meet the conditions for HW equilibrium?

Answer 7

never

But it is useful for predicting genotype frequencies from allele frequencies

patterns of deviation from the model help identify mechanisms of evolutionary change.

Question 8

If certain conditions are met

Answer 8

the genetic structure of a population does not change over time.

Question 9

Conditions that must be met for Hardy–Weinberg equilibrium:

Answer 9

No mutation
No selection among genotypes
No gene flow
Population size is infinite 
random mating

Question 10

Kuru

Answer 10

heterozygote advantage

Kuru is an acquired prion disease largely restricted to the Fore linguistic group of the Papua New Guinea Highlands

Heterozygosity for a common polymorphism in the human prion protein gene (PRNP) confers relative resistance to prion diseases.

Kuru imposed strong balancing selection on the Fore, essentially eliminating PRNP 129 homozygotes

Question 11

Malaria heterozygote advantage

Answer 11

People who carry one copy of the S allele are more likely to survive malaria than AA homozygotes.

The higher fitness of AS heterozygotes favors a balance between the 2 alleles; balancing selection.

Question 12

fitness

Answer 12

The contribution of a genotype or phenotype to the genetic composition of subsequent generations, relative to the contribution of other genotypes or phenotypes.

Question 13

RXFP2

Answer 13

In wild Soay sheep, large horns confer an advantage in strong intra-sexual competition, yet males show an inherited polymorphism for horn type.

Genetic variation in this trait is maintained by a trade-off between natural and sexual selection at a single gene, relaxin-like receptor 2 (RXFP2)

An allele conferring larger horns, Ho+, is associated with higher reproductive success

a smaller horn allele, HoP, confers increased survival, resulting in a net effect of overdominance (that is, heterozygote advantage)

Question 14

nonrandom mating

Answer 14

The phenomenon in which individuals select mates based on their phenotypes or genetic lineage.

WILL NOT CHANGE ALLELE FREQUENCIES

Question 15

inbreeding

Answer 15

) increases the frequency of homozygotes and reduces the frequency of heterozygotes in each generation.

does not cause evolution, because allele frequencies do not change.

change genotype frequencies

Question 16

inbreeding depression

Answer 16

a decline in average fitness that takes place when homozygosity increases and heterozygosity decreases in a population

Question 17

inbreeding depression results from two processes

Answer 17

Many recessive alleles represent loss-of-function mutations

increases the frequency of homozygous recessive individuals and thus the frequency of individuals expressing the mutation.

Many genes—especially those involved in fighting disease—are under intense selection for heterozygote advantage. If an individual is homozygous at these genes, then fitness declines.

Question 18

Random genetic drift

Answer 18

a change in genetic variation from generation to generation due to random sampling error.

. Allele frequencies may change as a matter of chance.

This is more likely to occur in a small population

Question 19

mutation

Answer 19

origin of genetic variation.
any change in the nucleotide sequences of DNA.
random with respect to the needs of an organism;
selection acting on the random variation results in adaptation.

Question 20

characteristics of mutation

Answer 20

Most mutations are harmful or neutral.

A few are beneficial; or if conditions change, a mutation could become advantageous.

Mutations can also restore genetic variation that other processes have removed.

can be very high, as in viruses; or quite low as in some eukaryotes.

Question 21

Ara-3

Answer 21

After 31,000 generations, one strain of bacteria, Ara-3 had evolved a new way to nourish themselves

, they drew on a different energy source in their medium, citrate.

Ara-3 eventually evolved the ability to use it with oxygen present (Cit+ cells

Question 22

gene flow

Answer 22

a result of the migration of individuals and movement of gametes between populations.

New individuals can add alleles to the gene pool or change allele frequencies

reduces genetic differences among populations

Question 23

genetic drift

Answer 23

results from random changes in allele frequencies.

Harmful alleles may increase in frequency, and rare advantageous alleles may be lost.

also possible that advantageous alleles may be introduced.
In small populations, genetic drift can be significant.

Question 24

founder effect

Answer 24

colonizing population is unlikely to have all the alleles present in the whole population.

Question 25

Brown anole lizard

Answer 25

populations were established on seven small islands in the Bahamas from the same large-island source

generated significant among-island genetic and morphological differences that persisted

All populations adapted in the predicted direction (i.e., shorter hindlimbs) in response to the narrower vegetation on the small islands

Both founder effects and natural selection jointly determine trait values in these populations

Question 26

bottleneck effect

Answer 26

Environmental conditions result in survival of only a few individuals.

Species with low genetic variation.

greater prarie chickens and california fan palms

Question 27

stabilizing selection

Answer 27

preserves the average phenotype.

reduces variation but does not change the mean.

Natural selection is often stabilizing (rates of evolution are slow).
ex: human birth weights

Question 28

Directional selection

Answer 28

favors individuals that vary in one direction

When individuals at one extreme are more successful.

results in an increase of the frequencies of alleles that produce the favored phenotype

positive selection

Question 29

disruptive selection

Answer 29

favors individuals that vary in both directions from the mean.

variation in a population is increased

Question 30

If directional selection operates over many generations

Answer 30

an evolutionary trend occurs.

Question 31

Horns of Texas Longhorn cattle

Answer 31

have evolved through directional selection; predation was the selection pressure

Longer horns were advantageous for defending young calves from attacks by predators, so feral herds of Spanish cattle developed much longer horns between the early 1500s and the 1860s

Question 32

Baleen whales

Answer 32

directional selection

) underwent a clade-wide shift in their mode of body size evolution during the Plio-Pleistocene.

temporally linked to the onset of seasonally intensified upwelling along coastal ecosystems.

Question 33

stabilizing selection is often called

Answer 33

purifying selection because there is selection against any deleterious mutations.

Question 34

black-bellied seed crackers

Answer 34

its bill size is influenced by disruptive selection

Birds with large bills can crack the hard seeds of a sedge. Birds with small bills feed more efficiently on soft seeds of a different sedge species.

Birds with intermediate sized bills cannot use either kind of seed efficiently and survive poorly.

Question 35

soapberry bugs

Answer 35

use their “beak” to feed on seeds within fruits

feed most effectively when their beak length is similar to the depth of the seeds within the fruit

In southern Florida, soapberry bugs feed on the larger fruit of balloon vines; they have longer beaks

In central Florida, they feed on the smaller fruit of introduced goldenrain trees; they have shorter beaks

Question 36

frequency dependent selection

Answer 36

A polymorphism can be maintained when fitness depends on its frequency in the population.

Example: A scale-eating fish in Lake Tanganyika. “Left-mouthed” and “right-mouthed” individuals are both favored; the host fish can be attacked from either side.