BIOL 206 Midterm: BIOL206 MIDTERM 2

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oliveant740

13 Dec 2015

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Week 5, lecture 11: evolution at multiple loci: linkage. Two loci in a population are in linkage equilibrium when the genotype of a chromosome at one locus is independent of its genotype at the other locus. Chromosome observed frequencies: frequency of ab = frequency. A frequency b: d (a. k. a the coefficient of linkage disequilibrium) is equal to 0: D = (f [ab] * f [ab]) (f [ab] * f [ab]) Linkage disequilibrium (ld) is the non-random association of alleles at two or more loci. Selection at one locus can affect other loci (knowing the genotype of a chromosome at one locus provides a clue about the genotype at the other) By extension of the hardy-weinberg theorem, the. Population 1 is in linkage equilibrium (under hwe and no linkage) This can be extended to genotypes: 4 chromosomes yield 10 genotypes. Deviations from ld can be tested using x2 tests. E. g. human hair and eye colour, nostril flaring, tongue rolling.

Related Questions

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. In a tropical human population in Hardy-Weinberg equilibrium for an autosomal locus determining the presence of pigment in the skin, the frequency of albinism (aa) is 1 in 10,000. What is the approximate frequency of the heterozygotes (Aa)? Please show your work.

2. Variation in horn length in rhinoceros beetles results from allelic variation in a single gene. Assume Hardy-Weinberg equilibrium and determine the allelic frequencies of L1, L2 and L3, genotypic frequencies of long-horned, short-horned and absent-horned beetles in this population. Please show your work.

Genotype Phenotype N

L1/L1

L1/L2 LONG 7500

L1/L3

L2/L2

L2/L3 SHORT 2100

L3/L3 ABSENT 400

3. In a population of African Black Mamba snake, one locus A on chromosome 5 has been found responsible for the aggressive phenotype. It appears that the aggressive phenotype is greatly associated with the body length phenotype locus B, which present in the adjacent locus on chromosome 5. Determine the relationship between these loci using the population data given below. Are these two loci in linkage equilibrium? If not, what is the disequilibrium value for this population? Please show your work

Haplotype N

A1B1 200

A1B2 50

A2B1 100

A2B2 650

limegnu434

2. Consider two gene loci in the mouse, locus1 and locus 2. Each locus is on a different, nonhomologousautosomal chromosome . Alleles at locus 1 influence fur color.Allele A is for black and allele a is for white.Allele A is completely dominant to allele a . Allelesat locus 2 influence stature; allele B is for tall andallele b is for short. Allele B is completelydominant to allele b.

Mouse 1, genotype Aa Bb, mates withfemale mice , genotype Aa Bb; 100 progeny are produced.

___: What fraction of the gametes from mouse 1is expected to be genotype Ab ?

___: What fraction of the gametes from mouse 1is expected to have allele a ?

___: What fraction of the progeny is expectedto be true-breeding for both stature and black fur?

___: How many progeny are expected to be tallwith white fur? Show your calculations.

___: How many progeny are expected to beheterozygous at both loci? Show yourcalculations.

___: If you randomly choose two progeny mice,one at a time, what is the probability that both mice are tall andwhite? Show your calculations.

3. Using the geneloci, alleles and phenotypes as described in question 2, considerthis mating between Mouse 3, black and tall, and mouse 4, black andtall. That mating produced these progeny: 58 black and short, 165black and tall, 25 white and short, 62 white and tall.

____: what is the expectednumber of progeny of the phenotypic class, black and short?Show your work.

____: What is the Chi-squarevalue for these observed and expected data? Show yourwork.

___: How many degrees offreedom are used for the Chi-square test in thissituation?

______: What is theapproximate Chi-square probability for this Chi-square value anddegrees of freedom?

_____: Mouse 3 mated withmice that had the phenotype short & white, and produced 200progeny. How many progeny are expected to have the phenotype, blackand tall?

____: In addition tothe gene loci, alleles and phenotypes described in question 1,consider a third gene locus with alleles D and d; D for long fur,and d for short fur. D is completely dominant to allele d. Thisgene locus segregates independently of the other two loci. Mouse 5,genotype Aa Bb Dd, mates with mouse 6 of the same genotype.What fraction of the progeny are expected to have the phenotype,black fur, tall & long fur?

I don't need the answers to question #2, justquestion #3. (the hilghted) However question 3 asks for informationfrom question 2, so that is why it is there

Thank you

plumbuffalo108

BIOL 206 Midterm: BIOL206 MIDTERM 2

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