PCB 3063 Lecture Notes - Lecture 34: Zygosity, Genotype, Growth Medium

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2 Apr 2018

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True or false: the greater distance between the two loci, the higher probability of crossing over. In recombination (crossing over) occurs in two-point mapping, the progeny will include both ________ and _____________ phenotypic combinations. Map units are relative measurements of distance based on recombination frequencies, not _________ What are the three points of criteria for three point mapping: genotype of organism must be heterozygous for all three genes. 2. cross must be designed in a way that the genotype can be accurately determined by examining the phenotype. 3. a sufficient number of offspring for a sample of all crossover possibilities. Crossing a heterozygous for all three loci with a homozygous mutant for all three loci. Steps for three point mapping: group offspring into pairs and phenotypic categories. What is the allele frequency equation? p(a) + q(a) = 1. What is the genotypic frequency equation (hardy weinberg law)? p(2) (aa) + 2pq (aa) + q(2) (aa) = 1.

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ANSWER ALL the PARTS you can

PART1 Alleles are considered linked if recombination is less than 50% in:

a) a Px P Fl cross

b) an F1 x F1F2 cross

c) an F2 x F2F3 cross

d) an Fl x homozygous recessive cross

e) any F2 progeny x homozygous recessive cross 1.

PART2 If two loci A/a B/b are 9 map units apart, and an Ab/aB individual is testcrossed,

a) There will be 9% AB individuals

b)There will be 91% Ab individuals

c) There will be 4.5% ab individuals

d) There will be 91% recombination individuals

If two genes a and b show 50% recombination genes a and c show 35% recombination, and genes b and show 32% recombination, then

a) Genes a and b are on the same chromosome, and 50 m.u. apart

b) Genes a and b are on different chromosomes

c)Genes a and b are on the same chromosome, and 67 map units apart

d) One cannot tell if genes a and b are on the same or different chromosomes from given data.

PART4 If two genes a and b are 8.3 m.u. a part, one expects to find

a) 8.3% recombinant gametes from a double heterozygous parent

b) 91.7% recombinant gametes from a double heterozygous parent

c) A chiasma between the a and b loci in 8.3% of the meiosis

d) A chiasma between the a and b loci in 91.7% of the meiosis.

PART5 Map distances are most accurate when genes are closely linked because as genes become further apart,

a) They always show independent assortment

b)The chance of multiple crossovers increases

c) They no longer recombine

d) There is chiasma interference

PART6 In a three-point testcross, the most frequent classes of progeny were ABc and abC. The less frequent classes of progeny were AbC and aBc. Which gene is in the middle?

a) Aa

b) B/b

c)C/c

d) It is not possible to tell from just these data

PART7 In a three-point testcross with 100 progeny, there were 16 single crossovers between genes A and B, 29 single crossovers between genes B and C, and 4 double crossovers. The correct gene order was determined to be A-B-C. What is the map distance between A and B?

a) 20%

b) 0.2 m.u

c) 20 m.u.

d) 16 m.u.

e) 29 m.u.

f) 16%

Below are data from a three-point linkage experiment in Drosophila melanogaster. These data represent the offspring from a testcross between flies expressing the recessive mutant phenotypes for black body, vestigial wings and brown eyes and flies that express normal wild type phenotypes but are heterozygous for all three traits. All the heterozygous wild type parental flies in this cross start out with mutant alleles in the cis configuration. Answer the following questions based on these data and show your work for question 1 (a-d).

Body	Wing	Eye	Phenotype	Count
b⁺	vg⁺	bw⁺	Gray body, normal wings, red eyes	103
b	vg	bw	Black body, vestigial wings, brown eyes	95
b⁺	vg	bw	Gray body, vestigial wings, brown eyes	32
b	vg⁺	bw⁺	Black body, normal wings, red eyes	29
b⁺	vg⁺	bw	Gray body, normal wings, brown eyes	71
b	vg	bw⁺	Black body, vestigial wings, red eyes	68
b⁺	vg	bw+	Gray body, vestigial wings, red eyes	10
b	vg⁺	bw	Black body, normal wings, brown eyes	13

1a)Which combinations of phenotypes are only possible in those offspring derived from gametes resulting from double crossover events?

_________________________________________________________________________________________

1b)What is the distance between the body color (gray vs. black) and wing loci (normal vs. vestigial)?

1c)What is the distance between the body color (gray vs. black) and eye color loci (red vs. brown eyes)?

1d)What is the coefficient of coincidence for double crossovers?

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

PCB 3063 Lecture Notes - Lecture 34: Zygosity, Genotype, Growth Medium

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