Study Guide 6 Hardy Weinberg

Question 1

A small population of 26 individuals has give alleles, A, B, C, D, and E for a particular gene.
-Five individuals are DA heterozygotes
-Five individuals are AA homozygotes
-Five individuals are AB heterozygotes,
-Five individuals are CD heterozygotes
-Five individuals are CC homozygotes
-One individual is an EE homozygote

a) what is the frequency of each allele in this population?

Answer 1

A allele: 0.3846
B allele: 0.0962
C allele: 0.2885
D allele: 0.1923
E allele: 0.0385

Question 2

A small population of 26 individuals has give alleles, A, B, C, D, and E for a particular gene.
-Five individuals are DA heterozygotes
-Five individuals are AA homozygotes
-Five individuals are AB heterozygotes,
-Five individuals are CD heterozygotes
-Five individuals are CC homozygotes
-One individual is an EE homozygote

b) if five AE heterozygotes migrate into the population, what will be the resulting allele frequencies?

Answer 2

A allele: 0.4032
B allele: 0.0806
C allele: 0.2419
D allele: 0.1613
E allele: 0.1129

Question 3

A population of otters in H-W equilibrium has two alleles for fur color: D is dark brown and complete dominant to d, which is light brown.
-If 81% of the population has light brown fur, what is the frequency of homozygous dominant otters

Answer 3

0.01

Question 4

A population of plants in H-W equilibrium has two alleles (B an b) for flower color. The frequency of the B allele in the population is 0.7.
-What is the frequency of plants in this population that are heterozygous for flower color?

Answer 4

0.42

Question 5

A nearby population of snails in H-W equilibrium has two alleles (R and r) for shell color.
-If frequency of snails that are homozygous for R is 0.64, what is the frequency of snails that are homozygous for r?

Answer 5

0.04

Question 6

A population of trees in H-W equilibrium has two alleles (F and f) for seed color. The frequency of trees heterozygous for seed color is 0.42. You know that the f allele is more common than the F allele in this population.
-What are the frequencies of each allele in this population?

Answer 6

p(F) = 0.3 and q(f) = 0.7

Question 7

A population of geckos in H-W equilibrium has two alleles for tail length: L for long tails, which is incomplete dominant to l for short tails. the frequency of geckos with long tails is 0.36
-What percent of the population would expect to be heterozygous?

Answer 7

0.48

Question 8

A population of bison in H-W equilibrium has three alleles for horn shape: long (A), short (a), and curly (α). The long allele is dominant over both the short and curly alleles, and the short allele is dominant over the curly allele. the frequency of the a allele is 0.5, and 16% of the population has curly horns.

a) what percent of the population has long horns?

Answer 8

0.19

Question 9

A population of bison in H-W equilibrium has three alleles for horn shape: long (A), short (a), and curly (α). The long allele is dominant over both the short and curly alleles, and the short allele is dominant over the curly allele. the frequency of the α allele is 0.5, and 16% of the population has curly horns.

b) which of the three phenotypes (long, short, curly) is the most common in this population?

Answer 9

short

Question 10

A population of bison in H-W equilibrium has three alleles for horn shape: long (A), short (a), and curly (α). The long allele is dominant over both the short and curly alleles, and the short allele is dominant over the curly allele. the frequency of the α allele is 0.5, and 16% of the population has curly horns.

c) what is the frequency of homozygotes in this population?

Answer 10

0.42

Question 11

Given the following genotype frequency, is each of these populations in Hardy-Weinberg equilibrium? If not, determine which observed genotype frequencies are greater or less than expected and propose an explanation for the observed phenotypes

a) AA = 0.01, Aa = 0.18, aa = 0.81

Answer 11

in HWE

Question 12

Given the following genotype frequency, is each of these populations in Hardy-Weinberg equilibrium? If not, determine which observed genotype frequencies are greater or less than expected and propose an explanation for the observed phenotypes

b) AA = 0.25, Aa = 0.50, aa = 0.25

Answer 12

in HWE

Question 13

Given the following genotype frequency, is each of these populations in Hardy-Weinberg equilibrium? If not, determine which observed genotype frequencies are greater or less than expected and propose an explanation for the observed phenotypes

c) AA = 0.36, Aa = 0.60, aa = 0.04

Answer 13

not in HWE, excess of heterozygotes; potential causes: outbreeding, natural selection (stabilizing), or potentially short-term drift (long term, drift causes excess of one homozygote)

Question 14

Given the following genotype frequency, is each of these populations in Hardy-Weinberg equilibrium? If not, determine which observed genotype frequencies are greater or less than expected and propose an explanation for the observed phenotypes

d) AA = 0.09, Aa = 0.42, aa = 0.49

Answer 14

in HWE

Question 15

Given the following genotype frequency, is each of these populations in Hardy-Weinberg equilibrium? If not, determine which observed genotype frequencies are greater or less than expected and propose an explanation for the observed phenotypes

e) AA = 0.64, Aa = 0.20, aa = 0.16

Answer 15

not in HWE, excess of homozygotes; potential causes: inbreeding, natural selection (diversifying), or potentially short-term drift (long term, drift causes excess of one homozygote)

Question 16

How are the founder effect and a population bottleneck similar? How are they different? Which one would you predict to have more serious negative impact on the species as a whole?

Answer 16

founder event
-reduces the gene pool by decreasing population size
-original larger population still exists
-maintains genetic diversity
-can contribute diversity to the new population through migration

bottleneck event
-also reduces the gene pool by decreasing population size
-only the small remaining population persists
-limited genetic diversity in the surviving population
-more likely to have severe negative effects on the species

Question 17

Describe the consequences of genetic drift.

Answer 17

-reduces genetic diversity (loss/fixation of alleles)

-increases inbreeding and homozygosity

-raises deleterious recessive conditions

-increases susceptibility to stressors (disease, climate change)

Question 18

Why are small populations more affected by grift than large populations?

Answer 18

-fewer chances for rare alleles to be passed on

-example: in a population of 500 (allele freq 0.001), only 1 carriers it. if that individual doesn’t reproduce the allele is lost

-in a population of 500,000, more carries increasing passing likelihood

Question 19

Gene flow and genetic drift are sometimes referred to as ‘non-adaptive evolution.’ What does this phrase mean? what type(s) of evolution is/are adaptive?

Answer 19

-Non-adaptive evolution: genetic change that does not benefit survival or reproduction

-adaptive evolution: only through natural selection, which favors beneficial genotypes/phenotypes

-random changes: other processes (ex genetic drift) can be random and may harm the population

-example: in small populations, genetic drift can increase deleterious alleles, even against natural selection

Question 20

Describe the genetic mechanism by which inbreeding increases homozygosity in a population.

Answer 20

-inbreeding is mating between individuals with similar genotypes/phenotypes

-homozygous matings:
dominant x dominant: all dominant offspring
recessive x recessive: all recessive offspring

-heterozygote mating:
50% hetero, 25% homo dominant, 25% homo recessive

-outcome: each generation, half of the heterozygotes shift to homozygous, leading to the eventual loss of heterozygotes.

Question 21

If a population of plants begins with two alleles being equally common (p=0.5 and q=0.5) and all plants self-fertilize, what would you expect the frequency of heterozygotes to be in the first generation? in the 50th? in the 100th?

Answer 21

The equation is the starting frequency to the power of the generation:
(0.5)^50= 8.8818 e -16
and (0.5)^100=7.889 e -31

Question 22

Describe the genetic mechanism by which inbreeding increases homozygosity in a population.(not asked here)

b)After how many generations would you predict there will be no heterozygotes in the population?

Answer 22

heterozygote loss prediction:
-never reaches 0: heterozygote frequency decreases by half each generation

-imminent loss: when the expected number of heterozygotes is less than one, loss is imminent

-population size impact: the timing of this loss depends on population size

Question 23

We listed five conditions that a population must meet in order to be in Hardy-Weinberg Equilibrium, how might violation of one assumption lead to or be affected by violations of other assumptions? for example, how might natural selection affect the fate of a new mutation in a population?

Answer 23

mutation effects
-beneficial alleles: may increase in frequency due to natural selection

-deleterious alleles: may decrease in frequency due to natural selection

-genetic drift: can lead to loss of mutations in the next generation, regardless of status

-migration: mutations can spread to other populations

-reproductive impact: may affect mating randomness (ex attractiveness mating capability)

Question 24

In humans, hemophilia (a blood disorder that prevents blood clotting) is cased by a recessive allele on the X-chromosome. Hemophilia is extremely rare; only 0.01% of men are affected by the disease. for this question assume that humans are in H-W equilibrium.

a) what is the frequency of the hemophilia allele in humans?

Answer 24

-frequency of XaY: 0.0001

-HWE assumptions: allele is evenly distributed across all demographics (males and females)

-overall frequency: q = 0.0001 in the entire population, including both sexes

Question 25

In humans, hemophilia (a blood disorder that prevents blood clotting) is cased by a recessive allele on the X-chromosome. Hemophilia is extremely rare; only 0.01% of men are affected by the disease. for this question assume that humans are in H-W equilibrium.

b) what frequency of women would you expect to have hemophilia?

Answer 25

q2 = (0.0001)^2 = 0.00000001

Question 26

The figure shows observed and expected genotype frequencies for a population of Avena fatua grass

a) is this population in H-W equilibrium? if not, describe what assumptions of H-W equilibrium could be violated in this population

Answer 26

No not in HWE

observed vs expected frequencies
-observed frequencies (in green) differ significantly from expected HWE frequencies (in purple)

-homozygous genotype frequencies are much higher than expected

-heterozygotes frequencies are much lower than expected

-possible causes: inbreeding, diversifying selection, and migration (immigration of homozygotes or emigration of heterozygotes)

Question 27

The figure shows observed and expected genotype frequencies for a population of Avena fatua grass

b) are the two genes experiencing the same pattern? how does your answer to that question narrow down the possible options you listed in part A?

Answer 27

Given that both genes are experiencing the same pattern, inbreeding is a little more likely than diversifying selection or migration operating similarly at both genes. All are still possible.

Question 28

The table below shows the genotype frequencies for a particular gene observed in a fictional population of otters, and the expected phenotype frequencies in this population was in H0W equilibrium. What violations of HWE conditions could be affecting this population? select all that apply

a) migration of rr individuals out of the population
b) genetic drift increasing the frequency of the R allele
c) inbreeding
d) directional selection in favor of the RR phenotype
e) mutation of R alleles in r alleles

Answer 28

a) migration of rr individuals out of the population
b) genetic drift increasing the frequency of the R allele
d) directional selection in favor of the RR phenotype