PCB 4674 Study Guide - Midterm Guide: Sexual Reproduction, Meiosis, Red Queen Hypothesis

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orchidbeaver616

14 Oct 2016

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Chapter 8: evolution at multiple loci: linkage and sex. Linkage equilibrium: the genotype of a chromosome at one locus is independent of its genotype at the other locus: the following conditions are true for a pair of loci if they"re in linkage equilibrium: The frequency of b on chromosomes carrying allele a is equal to the frequency of b on chromosomes carrying allele a. The frequency of any chromosome haplotype can be calculated by multiplying the frequencies of the constituent alleles. Example: the frequency of ab chromosomes can be calculated by multiplying the frequency of allele a and the frequency of allele b. The quantity d (coefficient of linkage disequilibrium) is equal to zero. Linkage disequilibrium: when there is a nonrandom association between a chromosome"s genotype at one. Population admixture: eliminating linkage disequilibrium: sexual reproduction (meiosis with crossing over and outbreeding) Genetic hitchhiking: because of linkage disequilibrium, single-locus studies can yield misleading conclusions.

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1) In a randomly mating population of fence lizards, haplotype frequencies at the A and B loci are as follows: 60% AB, 10% aB, 10% Ab, 20% ab.

a) Calculate the coefficient of linkage disequilibrium in this population.

b) From your answer, can you infer whether the A and B loci are on the same chromosome?

c) If the population had the same allele frequencies but no linkage disequilibrium, what would be the frequency of the AB haplotype?

blushguinea-pig707

Need help with evolution questions:

1.) A haplotype is best defined as the ________________.

	haploid genotypes of all the gametes produced by a diploid individual

ABO blood type conferred by an individual gamete

genotype of either the paternal or maternal chromosomal complement

multilocus genotype of a chromosome or gamete

2.) Which of the following statements regarding linkage disequilibrium is true?

Exists when D is less than zero, but not when it is greater than zero.

Is reduced by sexual reproduction.

Is increased by crossing-over during meiosis.

Is increased by any random sampling error that happens to create or destroy certain chromosome genotypes but not others.

Is reduced by selection that favors certain combinations of genotypes.

3.) Selection on multilocus genotypes in random-mating populations leads to linkage disequilibrium when _______________.

it reduces mutation rates

it eliminates all haplotypes from the population

it prevents crossing-over during meiosis

some allele combinations confer greater fitness than do others

4.) When two loci are in linkage equilibrium, the allele carried on a chromosome at one locus is independent of the allele carried on the chromosome at another locus. When this is the case, _________________.

allele frequencies will not change over time

the two loci (or, more specifically, their protein products) do not interact

the frequency of each haplotype can be calculated by multiplying the frequency of its two alleles

all possible haplotypes occur at equal frequency

5.) Which of the following accurately characterize(s) Muller's ratchet model for the selective advantage of sexual reproduction?

Drift establishes linkage disequilibrium because multilocus genotypes with few mutations are eliminated by chance events.

In populations without sexual reproduction, deleterious mutations accumulate, eventually imposing such a burden that the population goes extinct.

Sex is favored selectively because it recreates the zero-mutation genotypes lost due to drift.

All of the above correctly characterize Muller's ratchet model for the evolution of sexual reproduction.

6.) The genetic signature of recent positive selection on a locus is _______________.

high frequency and low linkage disequilibrium

low frequency and low linkage disequilibrium

low frequency and high linkage disequilibrium

high frequency and high linkage disequilibrium

7.) Sexual reproduction is advantageous both in changing environments and in constant environments, compared to asexual reproduction.

True

False

8.) Sexual reproduction causes genetic recombination via crossing-over, which combines genotypes from different parents.

True

False

9.) One reason sex may be maintained in natural populations is proposed by the "Red Queen Hypothesis", which states that.....

genotypes created by sex are created by natural selection over and over

recombination creating novel genotypes that can resist infection by parasites

mutation load is reduced by novel adaptive mutations

the ability of sex to fix multiple

1) With the following observed gametic frequencies (which are inlinkage disequilibrium), what is the frequency of theAB gamete type at equilibrium?
f(AB) = 0.07
f(Ab) = 0.21
f(aB) = 0.10 and
f(ab) = the remainder.

Hint : The frequency of the AB gamete type at equilibrium is theobserved frequency minus the coefficient of linkage disequilibrium.So f(AB) at equilibrium = f(AB) observed - d

The correct answer should be 0.05

2) After an exhaustive and expensive process togenotype individual spermatozoa for two loci, Cand D, a bleary-eyed researcher has determinedthat, out of 1,000 spermatozoa, the following gametes werepresent:
CD: 209
Cd: 307
cD: 307
and the remainder were cd.
Your job is to help the now delirious researcher to figure out ifthese loci are in linkage disequilibrium by calculating thecoefficient of linkage disequilibrium to two decimal places.

Hint : The coefficient of linkagedisequilibrium, d = ru - st where r = f(CD) = number of CD / 1,000,s = f(Cd) = number of Cd / 1,000, t = f(cD) = number of cD / 1,000and u = f(cd) = remainder / 1,000

The correct answer should be -0.06

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PCB 4674 Study Guide - Midterm Guide: Sexual Reproduction, Meiosis, Red Queen Hypothesis

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