Genetics: A Conceptual Approach

Benjamin Pierce

Chapter 25 Population Genetics - all with Video Answers

Educators

Chapter Questions

01:03

Problem 1

What is a Mendelian population? How is the gene pool of a Mendelian population usually described?

Magdalena Bentia

Numerade Educator

01:54

Problem 2

What are the predictions given by the Hardy-Weinberg law?

Magdalena Bentia

Numerade Educator

05:27

Problem 3

What assumptions must be met for a population to be in Hardy-Weinberg equilibrium?

Mathew Botros

Montclair State University

01:13

Problem 4

What is random mating?

Magdalena Bentia

Numerade Educator

02:13

Problem 5

Give the Hardy-Weinberg expected genotypic frequencies for (a) an autosomal locus with three alleles, and (b) an X-linked locus with two alleles.

Josee Pacheco

Numerade Educator

01:38

Problem 6

Define inbreeding and briefly describe its effects on a population.

Magdalena Bentia

Numerade Educator

01:59

Problem 7

What determines the allelic frequencies at mutational equilibrium?

Magdalena Bentia

Numerade Educator

01:14

Problem 8

What factors affect the magnitude of change in allelic frequencies due to migration?

Magdalena Bentia

Numerade Educator

03:19

Problem 9

Define genetic drift and give three ways in which it can arise. What effect does genetic drift have on a population?

Magdalena Bentia

Numerade Educator

02:59

Problem 10

What is effective population size? How does it affect the amount of genetic drift?

Magdalena Bentia

Numerade Educator

02:13

Problem 11

Define natural selection and fitness

Magdalena Bentia

Numerade Educator

11:15

Problem 12

Briefly describe the differences between directional selection, ovendominance, and underdominance. Describe the effect of each type of selection on the allelic frequencies of a population.

Mathew Botros

Montclair State University

03:13

Problem 13

What factors affect the rate of change in allelic frequency due to natural selection?

Mathew Botros

Montclair State University

06:05

Problem 14

Compare and contrast the effects of mutation, migration, genetic drift, and natural selection on genetic variation within populations and on genetic divergence between populations.

Mathew Botros

Montclair State University

05:38

Problem 15

How would you respond to someone who said that models are useless in studying population genetics because they represent oversimplifications of the real world?

Mathew Botros

Montclair State University

01:52

Voles (Microtus ochrogaster) were trapped in fields in southern Indiana and genotyped for a transferrin locus. The following numbers of genotypes were reconded, where $T^{\varepsilon}$ and $T^{*}$ represent different alleles.
$$\begin{aligned}
&\boldsymbol{T}^{\mathrm{E}} \boldsymbol{T}^{\mathrm{E}} \quad \boldsymbol{T}^{\mathrm{E}} \boldsymbol{T}^{\mathrm{F}} \quad \boldsymbol{T}^{\mathrm{F}} \boldsymbol{T}^{\mathrm{T}}\\
&407 \quad 170
\end{aligned}$$
Calculate the genotypic and allelic frequencies of the transferrin locus for this population.

Josee Pacheco

Numerade Educator

02:16

Problem 17

Jean Mann ing, Charles Kerfoot, and Edward Berger studied genotypic frequencies at the phosphoglucose isomerase (GPI) locus in the dadoceran Bosmina longirostris (a small crustacean known as a water flea). At one location, they collected 176 of the animals from Union Bay in Seattle, Washington, and determined their GPI genotypes by using electrophoresis (I. Manning. W. C Kerfoot, and E. M. Berger. 1978. Evolution $32: 365-374$ ).
Determine the genotypic and allelic frequencies for this population.

Josee Pacheco

Numerade Educator

00:02

Problem 18

Orange coat color of cats is due to an X-linked allele $\left(X^{O}\right)$ that is codominant with the allele for black $\left(X^{+}\right)$ Genotypes of the orange locus of cats in Minneapolis and St. Paul, Minnesota, were determined, and the following data were obtained:
Calculate the frequencies of the $X^{0}$ and $X^{+}$ alleles for this population.

Sana Riaz

Numerade Educator

00:02

Problem 19

Use the graph shown in Figure 25.3 to determine which genotype is most frequent when the frequency of the $A$ allele is:
a. 0.2
b. 0.5
c. 0.8

Sana Riaz

Numerade Educator

05:04

Problem 20

A total of 6129 North A mer ican Caucasians were blood typed for the MN locus, which is determined by two codominant alleles, $L^{\text {M }}$ and $L^{\text {N. }}$. The following data were obtained:
$$
\begin{array}{cc}
\text { Blood type } & \text { Number } \\
\mathrm{M} & 1787 \\
\mathrm{MN} & 3039 \\
\mathrm{N} & 1303
\end{array}
$$
Carry out a chi-square test to determine whether this population is in Hardy-Weinberg equilibrium at the MN locus.

Josee Pacheco

Numerade Educator

00:02

Problem 21

Assume that the phenotypes of lady beetles shown in Tigure 25.1 are encoded by the following genotypes:
a. For the lady beetles shown in the figure, calculate the frequencies of the genotypes and frequencies of the alleles.
b. Use a chi-square test to determine if the lady beetles shown are in Hardy Weinberg equilibrium.

Sana Riaz

Numerade Educator

02:59

Problem 22

Most black bears (Ursus americanus) are black or brown in color. However, occasional white bears of this species appear in some populations along the coast of British Columbia. Kemnit Ritland and his colleagues determined that white coat color in these bears results from a recessive mutation $(G)$ caused by a single nucleotide replacement in which guanine substitutes for aden ine at the melanocortin-1 receptor locus ( $m c r 1)$ the same locus responsible for red hair in humans (K. Ritland, C. Newton, and H. D. Marshall. 2001. Current Biology $11: 1468-1472)$. The wild-type allele at this locus $(A)$ encodes black or brown color. Ritland and his colleagues collected samples from bears on three islands and determined their genotypes at the $m c r 1$ locus.
a. What are the frequencies of the $A$ and $G$ alleles in these bears?
b. Give the genotypic frequendes expected if the population is in Hardy - Weinberg equilibrium.
c. Use a chi-square test to compare the number of observed genotypes with the number expected under Hardy-Weinberg equilibrium. Is this population in Hardy-Weinberg equilibrium? Explain your reasoning.

Josee Pacheco

Numerade Educator

04:16

Problem 23

Genotypes of leopard frogs from a population in central Kansas were determined for a locus (M) that encodes the enzyme malate dehydrogenase. The following numbers of genotypes were observed:
a. Calculate the genotypic and allelic frequencies for this population.
b. What would the expected numbers of genotypes be if the population were in Hardy-Weinberg equilibrium?

Josee Pacheco

Numerade Educator

00:51

Problem 24

Full color $(D)$ in domestic cats is dominant over dilute color $(d) .$ Of 325 cats obser ved, 194 have full color and 131 have dilute color.
a. If these cats are in Hardy-Weinberg equilibrium for the dilution locus, what is the frequency of the dilute allele?
b. How many of the 194 cats with full color are likely to be heterozygous?

Sana Riaz

Numerade Educator

01:42

Problem 25

Tay-Sachs disease is an autosomal recessive disorder. Among Ashkenazi Jews, the frequency of Tay-Sachs disease is 1 in $3600 .$ If the Ashkenazi population is mating randomly for the Tay-Sachs gene, what proportion of the population consists of heterozygous carriers of the Tay-Sachs allele?

Mathew Botros

Montclair State University

03:05

Problem 26

In the plant Lotus corniculatus, cyanogenic glycoside protects the plant against insect pests and even grazing by cattle. This glycoside is due to a simple dominant allele. A population of $L$ corniculatus consists of 77 plants that possess cyanogenic glycoside and 56 that lack the compound. What is the frequency of the dominant allde responsible for the presence of cyanogenic glycoside in this population?

Mathew Botros

Montclair State University

00:02

Problem 27

Color blindness in humans is an X-linked recessive trait. Approximately $10 \%$ of the men in a part icular population are color blind.
a. If mating is random for the color-blind locus, what is the frequency of the color-blind allele in this population?
b. What proportion of the women in this population are expected to be color blind?
c.What proportion of the women in the population are expected to be heterozygous carriers of the color-blind allele?

Sana Riaz

Numerade Educator

00:02

Problem 28

The human MN blood type is determined by two codominant alleles, $L^{\mathrm{M}}$ and $L^{\mathrm{N}}$. The frequency of $L^{\mathrm{M}}$ in Eskimos on a small Arct ic island is $0.80 .$
a. If random mating takes place in this population, what are the expected frequencies of the $\mathrm{M}, \mathrm{MN},$ and $\mathrm{N}$ blood types on the island?
b. If the inbreeding coefficient for this population is 0.05 what are the expected frequencies of the M, MN, and N blood types on the island?

Sana Riaz

Numerade Educator

14:15

Problem 29

Demonstrate mathematically that full-sib mating, $\left(F=^{1} /_{4}\right)$ reduces the heterozygosity by $^{1} /_{4}$ with each generation.

Mathew Botros

Montclair State University

01:12

Problem 30

The forward mutation rate for piebald spotting in guinea pigs is $8 \times 10^{-3} ;$ the reverse mutation rate is $2 \times 10^{-6}$. If no other evolutionary forces are assumed to be present, what is the expected frequency of the allele for piebald spotting in a population that is in mutational equilibrium?

Josee Pacheco

Numerade Educator

00:50

Problem 31

For three years, Gunther Schlager and Margaret Dickie estimated the forward and reverse mutation rates for five loci in mice that encode various aspects of coat color by examining more than 5 million mice for spontaneous mutations (G. Schlager and M. M. Dickie. $1966 .$ Science $151: 205-206$. The numbers of mutations detected at the dilute locus are as follows:
Calculate the for ward and reverse mutation rates at this Locus. If these mutations rates are representative of rates in natural populations of mice, what would the expected equilibrium frequency of dilute mutations be?

Sana Riaz

Numerade Educator

03:10

Problem 32

In Figure 25.10 , each blue dot represents one copy of the $A$ allele and each red dot represents each copy of the $a$ allele. Calculate the frequencies of the A allele in population II before and after migration. Explain why the frequency of $A$ in population II changed after migration.

Mathew Botros

Montclair State University

02:27

Problem 33

In German cockroaches, curved wing $(c v)$ is recessive to normal wing $\left(c v^{+}\right) .$ Bill, who is raising cockroaches in his dorm room, finds that the frequency of the gene for curved wings in his cockroach population is 0.6. In his friend Joe's apartment, the frequency of the gene for curved wings is $0.2 .$ One day Joe visits Bill in his dorm room, and several cockroaches jump out of Joe's hair and join the population in Bill's room. Bill estimates that, now, $10 \%$ of the cockroaches in his dorm room are individual roaches that jumped out of Joe's hair. What is the new frequency of curved wings among cockroaches in Bill's room?

Rashmi Sinha

Numerade Educator

03:19

Problem 34

A population of water snakes is found on an island in Lake Erie. Some of the snakes are banded and some are unbanded; banding is caused by an autosomal allele that is recessive to an allele for no bands. The frequency of banded snakes on the island is $0.4,$ whereas the frequency of banded snakes on the mainland is $0.81 .$ One summer, a large number of snakes migrate from the mainland to the island. After this migration, $20 \%$ of the island population consists of snakes that came from the mainland.
a. If both the mainland population and the island population are assumed to be in Hardy-Weinberg equilibrium for the alleles that affect banding, what is the frequency of the allele for bands on the island and on the mainland before migration?
b. After migration has taken place, what is the frequency
of the banded allele on the island?

Josee Pacheco

Numerade Educator

01:32

Problem 35

Pikas are small mammals that live at high elevation in the talus slopes of mountains. Most populations located on mountain tops in Colorado and Montana in North Amer ica are isolated from one another: the pikas dont occupy the low-elevation habitats that separate the mountain tops and don't venture far from the talus slopes. Thus, there is little gene flow between populations. Furthermore, each population is small in size and was founded by a small number of pikas. A group of population geneticists propose to study the amount of genetic variation in a series of pika populations and to compare the allelic frequencies in different populations. On the basis of the biology and distribution of pikas, predict what the population geneticists will find concerning the within-and between-population genetic variation.

Josee Pacheco

Numerade Educator

00:02

Problem 36

What proportion of the populations shown in Figure
25.13 reached fixation by generations $10,25,$ and $30 ?$ How does the proportion of populations that reach fixation due to genetic drift change over time?

Sana Riaz

Numerade Educator

01:51

Problem 37

In a large, randomly mat ing population, the frequency of the allele ( $s$ ) for sickle-cell hemoglobin is 0.028 . The results of studies have shown that people with the following genotypes at the beta-chain locus produce the average numbers of offspring given:
a. What will the frequency of the sickle-cell allele (s) be in the next generation?
b. What will the frequency of the sickle-cell allele be at equilibrium?

Sana Riaz

Numerade Educator

00:02

Problem 38

Two chromosomal inversions are commonly found in populations of Drosophila pseudoobscum: Standard (ST) and Arrowhead $(A R)$. When treated with the insecticide DDT, the genotypes for these inversions exh ibit overdominance, with the following fitnesses:
What will the frequencies of $S T$ and $A R$ be after equilibrium has been reached?

Sana Riaz

Numerade Educator

00:02

Problem 39

In a large, randomly mat ing population, the frequency of an autosomal recessive lethal allele is $0.20 .$ What will the frequency of this allele be in the next generation if the lethality takes place before reproduction?

Sana Riaz

Numerade Educator

00:44

Problem 40

The fruit fly Drosophila melanogaster normally feeds on rotting fruit, which may ferment and contain high levels of alcohoL. Douglas Cavener and Michacl Clegg studied allelic frequencies at the locus for alcohd dehydrogenase (Adh) in experimental populations of
D. melanogaster (D. R. Cavencr and M. I. Clegg 198 L. Evolution 35:1-10). The experimental populations were established from wild-caught flies and were raised in cages in the laboratory. Two control populations (C1 and C2) were raised on a standard cornmealmolasses-agar diet. Two ethanol populations (E1 and $\mathrm{E} 2$ ) were raised on a cornmeal-molasses-agar diet to which was added $10^{\circ}$ ethanol. The four populations were periodically sampled to determine the alldic frequendes of two alleles at the alcohol dehydrogenase Iocus, $A d h^{\circ}$ and $A d h^{2}$. The frequencies of these alldes in the experimental populations are shown in the graph.
a. On the hasis of these data, what conclusion might you draw about the evolutionary forces that are affecting the Adh alleles in these populations?
b. Cavener and Clegg measured the viability of the different Adh genotypes in the alcohol environment and obtained the following value:
Using these relative viabilities, calculate relative fitnesses for the three genotypes, If a population has an init ial frequency of $p=f\left(A d n^{5}\right)=0.5,$ what will the expected frequency of $A d h^{\prime}$ be in the next generation on the basis of these fitness values?

Josee Pacheco

Numerade Educator

00:01

Problem 41

A certain form of congenital glaucoma is caused by an autosomal recessive allde. A sume that the mutation rate is $10^{-5}$ and that persons having this condition produce, on the average, only about $80 \%$ of the offspring produced by persons who do not have glaucoma.
a. At equilibrium between mutation and sciection, what will the frequency of the gene for congenital glaucoma be?
b. What will the frequency of the disease be in a randomly mating population that is at equilibrium?

Sana Riaz

Numerade Educator

01:55

Problem 42

Examine Figure $25.15 .$ Which evolutionary forces:
a. Cause an increase in genetic variation both within and between populations?
b. Cause a decrease in genctic variation both within and between populations?
c. Cause an increase in genetic variation within populations but cause a decrease in genct ic variation between populations?

Sana Riaz

Numerade Educator

00:01

Problem 43

The frequency of allele $A$ in a population is 0.8 and the frequency of allele $a$ is 0.2 . If the population mates randomly for this locus, give all the possible matings among the genotypes at this locus and the expected proportion of each type.

Sana Riaz

Numerade Educator

05:25

Problem 44

The Barton Springs salamander is an endangered species Sound only in three adjacent springs in the dity of Austin, Texas. There is growing concern that a chemical spill on a nearby freeway could pollute the spring and wipe out the spades. To provide a source of salamanders to repopulate the spring in the event of such a catastrophe, a proposal has been made to establish a captive breeding population of the salamander in a local zoo. You are asked to provide

Mathew Botros

Montclair State University

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