Deck 21: Population Genetics

Question 1

Which of the following is not a form of genetic drift?

A)Founder effect
B)Nonrandom mating
C)Population bottleneck
D)Heterozygote advantage
E)All of these are forms of genetic drift.

Answer 1

D

Question 2

Twenty loci are screened for genetic variation in a common caterpillar species.Four loci are found to have two or more alleles.The proportion of polymorphic loci for this population is thus

A)0.10.
B)0.20.
C)0.30.
D)0.40.
E)0.50.

Answer 2

B

Question 3

For which of the following traits is human mating expected to be nonrandom?

A)Blood type
B)Isocitrate dehydrogenase enzyme
C)Skin color
D)Presence or absence of a widow's peak
E)Fingerprint loci

Answer 3

C

Question 4

Synonymous mutations are found much more frequently than nonsynonymous mutations because

A)mutations do not occur randomly
B)the genetic code is redundant.
C)of genetic drift.
D)there is a selective advantage in looking like another species.
E)changes in the amino acid sequence of proteins are likely to be harmful.

Question 5

In a population of frogs,RR homozygotes produce an average of 5 offspring that survive to reproduce.Rr frogs produce 4,and rr frogs produce 1.The fitness of the three genotypes w₁₁,w₁₂,and w₂₂ are respectively

A)5,4,and 1.
B)0.5,0.4,and 0.1.
C)1.0.,0.8,and 0.2.
D)0.5,1.0,and 0.1.
E)None of these

Question 6

Genetic drift may lead to

A)loss of genetic variation in a population.
B)a decrease in the mutation rate of a particular gene.
C)increased heterozygosity at many loci.

Question 7

The

Question 8

A population genetic study of a certain insect revealed four alleles for the GPI (glucose-phosphate isomerase)locus.How many different genotypic classes should be found?

A)4
B)8
C)10
D)16
E)20

Question 9

When the population mean for a given measured trait is observed to decline over the course of several generations,it is an example of disruptive selection.

Question 10

For two populations to remain genetically homogenized,a significant proportion of the population of each must be exchanged at least every other generation.

Question 11

________ is the ultimate source of genetic variation in populations.

A)Natural selection
B)Genetic drift
C)Gene flow
D)Mutation
E)Recombination

Question 12

For a gene A, a geneticist studying a population of butterflies found the following genotypes: $\begin{array}{c}\begin{array}{r}108 \\144 \\48\end{array} \begin{array}{lll} \text {\( A A \) butterflies }\\ \text {Aa butterflies }\\ \text { aa butterflies}\end{array}\end{array}$


-What is the frequency of the a allele in the butterfly population?

A)0.16
B)0.04
C)0.40
D)0.64
E)0.40.

Question 13

Which of the following methods is least useful for assessing levels of genetic variation in populations?

A)DNA sequencing
B)VNTRs
C)Protein electrophoresis
D)Phenotypic observation
E)RFLP analysis

Question 14

Although bees carry pollen from tulip flowers to the blossoms on cherry trees,hybrid seeds are not produced because of

A)gametic isolation.
B)temporal isolation.
C)ecological isolation.
D)mechanical isolation.
E)All of these

Question 15

For a gene A, a geneticist studying a population of butterflies found the following genotypes: $\begin{array}{c}\begin{array}{r}108 \\144 \\48\end{array} \begin{array}{lll} \text {\( A A \) butterflies }\\ \text {Aa butterflies }\\ \text { aa butterflies}\end{array}\end{array}$


-What is the observed genotypic frequency of Aa individuals?

A)0.144
B)0.72
C)0.40
D)0.48
E)1.44

Question 16

In reciprocal hybrid crosses,the heterogametic sex is typically sterile while the homogametic sex is not.This phenomenon is referred to as

A)hybrid incompatibility.
B)postzygotic isolation.
C)Haldane's rule.
D)male sterility.
E)None of these

Question 17

Allele frequencies can change across the geographic range of a species according to climate,geological features,or direction in the range.For instance,a certain allele frequency might go up along with the elevation or down as you go south in the species' range.This systematic change in frequency is referred to as

A)genetic drift.
B)q².
C)directional selection.
D)a cline.
E)heterosis.

Question 18

If there are two alleles of a gene,B and b,and the frequency of the B allele (p)is 0.90,the frequency of the b allele (q)is

A)0.81.
B)0.30.
C)0.10.
D)0.09.
E)0.01.

Question 19

Heterozygotes for the sickle-cell allele show higher fitness than either homozygote genotype in malarial regions.This is an example of

A)epistasis.
B)pleiotropy.
C)founder effect.
D)overdominance.
E)codominance.

Question 20

Two populations experience equally severe bottlenecks,reducing each to one-tenth of its original size.One population is in the bottleneck for one generation,and the other is in the bottleneck for five generations.You assess the heterozygosity of both populations after they have been restored to their prebottleneck size.What do you expect to find,and why?

Question 21

Show algebraically that under Hardy-Weinberg equilibrium, allele frequencies will not change from one generation to another.

Question 22

Survival is the single most important process in evolution by natural selection.

Question 23

Two closely related insect species are active at different times of day,with one diurnal and the other nocturnal.This is an example of spatial isolation.

Question 24

Some recessive mutations can be exceedingly debilitating or lethal when expressed in homozygotes.If their effects are so severe,why doesn't natural selection simply purge such alleles from the population completely?

Question 25

The northern elephant seal,Mirounga angustirostris,suffered a significant population bottleneck in the late nineteenth century,when hunting reduced their population size to as few as 20 individuals.It has since rebounded to several tens of thousands.The related southern elephant seal,M.leonine,was not hunted as intensively.What prediction can you make about the relative levels of heterozygosity in populations of these two species?

Question 26

According to the Hardy-Weinberg principle, at equilibrium the allele frequencies are dependent on the genotypic frequencies.

Question 27

With respect to a gene with two alleles,for each generation of complete inbreeding the proportion of heterozygotes is expected to be reduced by while the proportion of each homozygous class is expected to increase in frequency by .Explain why this is so.

Question 28

The deciduous forest of eastern North America has experienced dramatic changes over the past two to three centuries,transitioning from a nearly continuous forested area to increasingly patchy areas of forest broken up by farming and development.Some species are more sensitive to severe habitat fragmentation than others.What are some characteristics that might make a species more susceptible to the effects of habitat and population fragmentation?

Question 29

Why do we expect that postzygotic isolation will evolutionarily precede prezygotic isolation in the speciation process?

Question 30

Red-green color blindness is an X-linked trait.In a population genetics study,1,000 people (500 men and 500 women)were tested for this trait,and 35 men were found to be color blind.Use this information to compute the frequency of the allele for color blindness and the wild-type allele in this population,and estimate the expected number of carrier females.

Question 31

In the early twentieth century,evolutionary biologists argued whether there was enough genetic variation in populations to explain the diversity of life by natural selection.With the advent of protein electrophoresis and DNA-level analysis,the problem turned on its head: the neutralist school arose from the idea that there was too much genetic variation to be maintained by natural selection.What are some of the arguments and observations neutralists cited to support the idea that much variation is neither favored nor disfavored by natural selection?

Question 32

Populations that suffer significant reductions in number may experience two population-genetic consequences that together can hasten their decline.Which two processes are likely to act in concert in small populations,and what is their effect?

Question 33

Observed genotypic frequencies in populations rarely match

Question 34

The frequency of a recessive X-linked allele is equal to the phenotypic frequency of males exhibiting that allele.

Question 35

In light of the fact that the assumptions of the

Question 36

Two neighboring Caribbean islands harbor iguana populations.One island (island A)has a total iguana population of 800,while the other (island B)has a population less than half that size,numbering 250.On island A,the frequency of an allele p is estimated at 0.75,while this same allele is present at a frequency of 0.90 on island B.During a hurricane tracking across the islands,a group of about 100 iguanas get rafted from island A to island B.What effect does this have on the frequency of allele p on island B?

Question 37

The genetic variation between human "races," such as Africans and Europeans,is greater than the variation within a single race.

Question 38

A selection coefficient of 1 means zero fitness.

Question 39

A gene is known to have three alleles: p,q,and r.The frequency of p is estimated at 0.70.Thus,the frequencies or q and r must be 0.15 each.

Question 40

This chapter discussed speciation by genetic divergence following geographic isolation,which is expected to lead to reduced gene flow,a process known as allopatric speciation.A more controversial form of speciation is the genetic divergence of populations without physical isolation,a process known as sympatric speciation.Can you envision a mechanism or process that would permit two coexisting populations of the same species to begin to diverge without being isolated from one another?

Question 41

Remote oceanic islands are characterized as having disharmonic biota,meaning the number and relative proportions of taxa living on the island differ significantly from the number and relative proportions of taxa on the nearest continental mainland area.Each island system is disharmonic in its own unique way.Why?