Deck 8: Evolution at Multiple Loci: Linkage and Sex

Question 1

Muller's ratchet posits that in a finite asexual population,the number of deleterious alleles will increase over time.The accumulation of these deleterious alleles is called ________.

A) inbreeding
B) linkage equilibrium
C) linkage disequilibrium
D) genetic load

Answer 1

D

Question 2

Research and analysis has documented that Muller's ratchet works ________.

A) in mathematical modeling
B) in empirical studies
C) in a natural setting
D) All of the above.

Answer 2

D

Question 3

The creation of new combinations of alleles,as a consequence of sexual reproduction with meiosis,is called ________.

A) genetic recombination
B) outcrossing
C) genetic drift
D) linkage disequilibrium

Answer 3

A

Question 4

Which of the following reduces linkage disequilibrium by disrupting overrepresented haplotypes and by generating new ones?

A) sexual reproduction
B) genetic recombination
C) crossing over
D) All of the above.

Question 5

Besides selection on multilocus genotypes,there are two other mechanisms that can create linkage disequilibrium.What are they?

Question 6

When genotypes at one locus of a chromosome are independent of genotypes at another locus of the same chromosome,the two loci are ________.

A) in linkage equilibrium
B) in linkage disequilibrium
C) nonrandomly associated
D) None of the above.

Question 7

A principle advantage of sexual reproduction is that it ________.

A) reduces linkage disequilibrium
B) helps to recreate genotypes that are either rare or missing in a population, but are favored by selection
C) regenerates genotypes in the evolutionary "arms race" between parasites and hosts
D) All of the above.

Question 8

Which of the following choices is NOT a potential disadvantage to sexual reproduction?

A) Finding a mate is energetically expensive.
B) Finding a mate may increase the risk of predation.
C) Copulation may not produce offspring.
D) Sexual reproduction reduces linkage disequilibrium.
E) None of the above.

Question 9

Which of the following conditions accurately represent Muller's ratchet,in terms of the selective advantage of sexual reproduction?

A) Deleterious mutations accumulate in asexual populations, resulting in a significant genetic load.
B) Sexual reproduction is selected because it reintroduces no-mutation genotypes that have been lost from the population.
C) Linkage disequilibrium increases in populations by genetic drift because no-mutation multilocus genotypes are lost by chance.
D) All of the above accurately represent the conditions of Muller's ratchet.

Question 10

According to the accompanying figure,we can conclude that ________.

A) the rate of decline in disequilibrium occurs more quickly with a lower rate of recombination
B) the rate of decline in disequilibrium occurs more slowly with a lower rate of recombination
C) the rate of decline in linkage disequilibrium is inversely proportional to the rate of recombination between them
D) None of these is an accurate statement.

Question 11

When considering two loci on a chromosome,the loci are said to be in ________,[two words] when the genotype at one locus is independent of the other.

Question 12

Alleles that are relatively new to a population and have been subject to positive natural selection are characterized by having ________.

A) high frequency and high linkage disequilibrium
B) high frequency and low linkage disequilibrium
C) low frequency and high linkage disequilibrium
D) low frequency and low linkage disequilibrium

Question 13

Certain loci that are in linkage disequilibrium with alleles of interest can be used as markers,which can then be useful in reconstructing the history of those alleles in populations.One such marker/allele is described in your text,where the allele in question has an insertion mutation,rendering an enzyme (glucocerebrosidase,or GBA)nonfunctional.The decay curve for linkage disequilibrium between this marker (named D1S305)and the nonfunctional GBA allele is shown in the accompanying figure.The orange lines show the present level of linkage disequilibrium and the inferred number of generations elapsed since the most recent common ancestor.Assuming an average generation time of 25 years,what is the best estimate for how long ago the most recent common ancestor existed?

A) about 55 years ago
B) about 1375 years ago
C) about 2325 years ago
D) There is insufficient data to make this determination.

Question 14

An advantage to studying linkage disequilibrium is that ________.

A) it provides another tool enabling the reconstruction of the history of genes and populations
B) it provides clear evidence of speciation events
C) it can be used to identify alleles that have been recently selected by natural selection
D) Both A and C.

Question 15

If there is a nonrandom association between the genotypes at two loci on a chromosome,the loci are said to be in ________.[two words]

Question 16

Which of the following can produce linkage disequilibrium?

A) genetic drift
B) selection on genotypes of more than one locus
C) mixing two disparate populations, each of which is in linkage equilibrium
D) All of these choices can create linkage disequilibrium.

Question 17

Certain loci that are in linkage disequilibrium with alleles of interest can be used as markers,which can then be useful in reconstructing the history of those alleles in populations.One such marker/allele is described in your text,where the allele in question has an insertion mutation,rendering an enzyme (glucocerebrosidase,or GBA)nonfunctional.The decay curve for linkage disequilibrium between this marker (named D1S305)and the nonfunctional GBA allele is shown in the accompanying figure.The orange lines show the present level of linkage disequilibrium and the inferred number of generations elapsed since the most recent common ancestor.Assuming an average generation time of 25 years,how many years total will be required for the linkage disequilibrium reach 0.2?

A) about 55 years total
B) about 100 years total
C) about 1000 years total
D) about 2500 years total
E) There is insufficient data to make this determination.

Question 18

Mathematical analysis of Muller's ratchet reveals that the most important parameter in the rate at which the ratchet works is ________.

A) population size
B) mutation rate
C) genetic heterogeneity
D) sexual/asexual reproductive ratio

Question 19

When genotypes at one locus of a chromosome are nonrandomly associated with the genotypes at another locus of the same chromosome,the two loci are ________.

A) in linkage equilibrium
B) in linkage disequilibrium
C) nonrandomly associated
D) None of the above.

Question 20

Haploid genotypes involving two loci,such as AB,Ab,aB,and ab,are known as an organism's ________.

Question 21

Drawing on the accompanying graphs for support,describe and explain the way in which Muller's ratchet works in asexual populations.

Question 22

Explain and describe the three ways in which linkage disequilibrium can be produced in a population.Refer to the accompanying figures to support your explanation.

Question 23

The principal advantage of sexual reproduction is that it "reshuffles the genetic deck." The creation of new combinations of alleles during sexual reproduction-complete with outbreeding and meiosis with crossing over-is called ________.[two words]

Question 24

In terms of population genetics,sexual reproduction on a functional level involves two necessary conditions.What are these conditions?

Question 25

In cases where a perpetual "arms race" occurs between biological antagonists,such as parasites and their hosts,sex is favored because it reduces linkage disequilibrium by recreating missing genotypes in an oscillating fashion.This hypothesis is called the ________ [two words] hypothesis.

Question 26

The mode of reproduction in which females produce genetically identical offspring from unfertilized eggs is known as ________.

Question 27

Please refer to the accompanying figures.Is the population in linkage equilibrium or linkage disequilibrium? Explain,drawing on the evidence in the figures.

Question 28

The observation that some organisms can (and do)produce both sexually and asexually within the same population produces some interesting questions,most notably the one Maynard Smith theorized about: Will one mode of reproduction replace the other over time? Explain Smith's assumptions,and compare the predictions made by Smith's model with what is actually observed in nature.Are either of these assumptions violated in real life? Why or why not?

Question 29

When a locus is discovered to be in linkage disequilibrium with nearby markers,and this allele is also found to occur in high frequency,it is logical to assume that this allele has been favored by ________.[two words]

Question 30

The explanation for the accumulation of deleterious alleles in asexual populations over time,with the resulting genetic load,is known as ________.[two words]