Question 1

A diploid plant is a trihybrid for flower color (gene "F"),leaf size (gene "L")and seed weight (gene "S");its phenotype includes red flowers,large leaves,and heavy seeds.This plant is crossed to a tester plant (which has white flowers,small leaves,and light seeds).The progeny is as follows:

$\begin{array}{|l|l|}
\hline23 \text { Red, heavy, large } & 232 \text { White, heavy, large } \
\hline 25 \mathrm{Red}, \text { heavy, small } & 228 \text { White, heavy, small } \
\hline 230 \mathrm{Red} \text {, light, large } & 25 \text { White, light, large } \
\hline 235 \mathrm{Red} \text {, light, small } & 26 \text { White, light, small }\
\hline
\end{array}$ 
What can be concluded about the linkage relationships of the three genes in question?
A)Genes F,L,and S are linked.
B)Genes F and L are linked,while S assorts independently.
C)Genes F and S are linked,while L assorts independently.
D)Genes S and L are linked,while F assorts independently.
E)Genes F,L,and S are unlinked and assort independently.

Accepted Answer

The progeny numbers suggest that genes F and S are linked, as the parental combinations (Red, heavy and White, light) are more frequent than the recombinant types, indicating linkage. Gene L shows independent assortment, as the large and small leaf phenotypes are evenly distributed among the progeny.

Question 2

In a diploid invertebrate,genes D and E are closely linked.Single crossovers between these two genes occurs only in 1 out of 40 meioses,and multiple crossovers are never observed.If an individual has the genotype D e/d E,what percentage of its gametes are expected to be recombinant (either DE or de)?
A)1.25%
B)2.5%
C)4%
D)5%
E)20%

Accepted Answer

Single crossovers between genes D and E occur in 1 out of 40 meioses, so the frequency of recombinant gametes (DE or de) is 1/40 = 2.5%.

Question 3

Out of 800 progeny of a three-point testcross,there were 16 double crossover recombinants,whereas 80 had been expected on the basis of no interference.The interference is:
A)0.690.
B)0.310.
C)0.155.
D)0.80.
E)0.40.

Accepted Answer

D

Question 4

The maize genes sh and bz are linked,40 map units apart.If a plant sh⁺bz/sh bz⁺ is selfed,what proportion of the progeny will be sh bz/sh bz? A)0.04 B)0.10 C)0.20 D)0.40 E)0.50

Accepted Answer

The genes are 40 map units apart, indicating a 40% recombination frequency. The non-recombinant (parental) gametes will be 60% of the total. Since sh bz/sh bz is a parental type, the probability of getting this genotype from selfing is (0.3 * 0.3) = 0.09, but since there are two ways to get sh bz/sh bz (from both parents), the final probability is 0.04.

Question 5

A male mouse of genotype A/a ^. B/b is testcrossed multiple times.Overall,these testcrosses produce 11 mice of phenotype A B,81 A b,77 a B,and 14 a b.Based on these data,the genotypes of the male mouse's parents are most likely: A)A/a;B/b and A/a;B/b. B)AB/AB and ab/ab. C)AB/ab and AB/ab. D)Ab/Ab and aB/aB. E)Ab/ab and Ab/ab.

Accepted Answer

The answer of A male mouse of genotype A/a ^....

Question 6

The F,G,and H loci are linked in the order written.There are 30 map units between F and G,and 30 map units between G and H.If a plant F G H/f g h is testcrossed,what proportion of progeny plants will be f g h/f g h if there is no interference?
A)0.70
B)0.30
C)0.245
D)0.21
E)0.15

Accepted Answer

The proportion of f g h/f g h progeny can be calculated considering the distances between the loci and using the formula for recombinant frequency. Since F and G, and G and H are each 30 map units apart, the probability of recombination between F and G is 0.30, and the same is true for G and H. For the progeny to be f g h/f g h, there must be no recombination between F and G, and between G and H, which occurs at a probability of (1 - 0.30) for each segment. Thus, the overall probability is (1 - 0.30) * (1 - 0.30) = 0.49 * 0.49 = 0.2401, which is approximately 0.245. This calculation assumes no interference, meaning the occurrence of a crossover in one region does not affect the probability of a crossover in an adjacent region.

Question 7

In Drosophila,the genes crossveinless-c and Stubble are linked,about 7 map units apart on chromosome 3.cv-c is a recessive mutant allele of crossveinless-c (cv-c⁺ is wild type),while Sb is a dominant mutant allele of Stubble (Sb⁺ is wild type). A dihybrid female Drosophila with genotype cv-c Sb⁺/cv-c⁺Sb is testcrossed.The proportion of phenotypically wild-type individuals in the progeny of the testcross will be: A)0.035. B)0.070. C)0.350. D)0.465. E)0.930.

Accepted Answer

The answer of In Drosophila,the genes crossveinless-c and Stubble are...

Question 8

The linkage relationships among the four mouse genes,A,B,C,and D,are shown in the map below.

What proportion of the eggs produced by a female mouse with genotype Ab/aB;CD/cd will carry all the recessive alleles?
A)0.064
B)0.075
C)0.150
D)0.250
E)0.255

Accepted Answer

The correct answer is A because the proportion of eggs carrying all the recessive alleles is 0.064. This can be calculated by multiplying the recombination frequencies between the genes. The recombination frequency between A and B is 30 mu, and the recombination frequency between B and D is 15 mu. Therefore, the recombination frequency between A and D is 30 mu + 15 mu = 45 mu. The proportion of eggs carrying all the recessive alleles is then (1 - 45 mu) = 0.064.

Question 9

In an experimental plant,the genes t and q are linked.A pure breeding t/t individual is crossed to a pure breeding q/q individual to obtain a dihybrid F₁.Genotypically,the F₁individuals can be described as: A)complementary dihybrids. B)crossover dihybrids. C)dihybrids in cis. D)recombinant dihybrids. E)dihybrids in trans.

Accepted Answer

The F1 individuals are dihybrids in trans because the genes t and q are linked and the alleles from each parent are on different homologous chromosomes.

Question 10

Two genes,A and B,are linked.An individual of genotype A b/A b is crossed to one that is a B/a B.The F₁ is selfed and an F₂ is obtained.Which of the following ratios most likely represents the phenotypic ratio observed in this F₂? A)1:1:1:1 B)1:4:4:1 C)9:3:3:1 D)51:24:24:1 E)66:9:9:16

Accepted Answer

Since genes A and B are linked, the phenotypic ratio in the F2 generation will deviate from the typical Mendelian 9:3:3:1 ratio. The 51:24:24:1 ratio reflects the linkage and recombination between the genes.

Question 11

A dihybrid in cis is crossed to a dihybrid in trans (the two genes of interest,A and B,are linked).What proportion of the progeny is expected to be homozygous recessive with respect to the two genes of interest?
A)less than 6.25%
B)more than 6.25%,but less than 18.75%
C)about 18.75%
D)more than 18.75%,but less than 37.5%
E)more than 37.5%

Accepted Answer

In a dihybrid cross involving linked genes, the proportion of progeny that are homozygous recessive for both genes is expected to be less than what would be predicted by independent assortment due to linkage. Since the genes are linked, recombinant types (which would include the double homozygous recessive type) are less common than parental types. The percentage given in choice A, less than 6.25%, reflects the reduced likelihood of obtaining a homozygous recessive individual for both traits due to this linkage, as 6.25% would be the expected proportion for each trait being homozygous recessive if the genes were assorting independently (1/16). With linkage, the actual proportion is even lower, especially in the absence of significant crossing over between the genes.

Question 12

Two genes,A and B,are linked.An individual of genotype A b/A b is crossed to one that is a B/a B.The F₁ is testcrossed.Which of the following ratios most likely represents the phenotypic ratio observed in the progeny of this testcross? A)1:1:1:1 B)1:4:4:1 C)9:3:3:1 D)51:24:24:1 E)66:9:9:16

Accepted Answer

The answer of Two genes,A and B,are linked.An individual of...

Question 13

A sweet pea plant of genotype A/A ^. B/B is crossed to one that is a/a ^. b/b to produce a dihybrid F₁.One cell of one F₁ individual (genotype A/a ^. B/b)goes through meiosis and produces four gametes of the following genotypes: A ^.b,A ^.b,a ^.B and a ^.B.What can be concluded regarding the linkage relationship between the two genes? A)Genes A and B are linked;the result is indicative of linkage as the gametes are recombinants. B)Genes A and B are linked;the result is indicative of linkage as the gametes are the products of crossovers. C)Genes A and B could be linked or unlinked;the result is not indicative of either,because in both cases it's possible to obtain 100% recombinant gametes from one meiosis. D)Genes A and B could be linked or unlinked;the result is unusual as we should never obtain more than 50% recombinants from one meiosis. E)Genes A and B are unlinked;the result is indicative of independent assortment as only two genotypes are represented among the gametes.

Accepted Answer

The result of obtaining 100% recombinant gametes from one meiosis is possible whether the genes are linked or unlinked, as it can occur due to independent assortment or a double crossover event.

Question 14

In Drosophila,the two genes w and sn are X-linked and 25 map units apart.A female fly of genotype w⁺sn⁺/w sn is crossed to a male from a wild-type line.What percent of male progeny will be w⁺sn? A)0% B)12.5% C)25% D)37.5% E)50%

Accepted Answer

The genes are 25 map units apart, indicating a 25% recombination frequency. In the cross, 50% of the male progeny will inherit the recombinant X chromosome (w+sn) from the female, and 25% of these will be w+sn due to recombination. Thus, 12.5% of the total male progeny will be w+sn.

Question 15

The mouse autosomal genes B and S are linked and 38 map units apart.Genotypes B S/B S and b s/b s are intercrossed,and the F₁ is testcrossed to b s/b s.The proportion of B-S- progeny will be: A)0.19. B)0.31. C)0.50. D)0.38. E)0.76.

Accepted Answer

Since the genes are 38 map units apart, the recombination frequency between them is 38/100 = 0.38. For the B-S- progeny, both the B and S alleles must have been lost through recombination. Therefore, the probability of producing a B-S- progeny is equal to the recombination frequency (0.38). In the testcross, the genotype of the F₁ parent is not relevant as it will always produce gametes containing either B or S. Thus, the proportion of B-S- progeny will be 0.38 multiplied by the proportion of b s gametes produced by the testcross parent. Since the testcross parent is homozygous for b s, it can only produce b s gametes. Therefore, the proportion of B-S- progeny will be 0.38 multiplied by 0.5 (since half the gametes produced by the testcross parent will be b s). Thus, the proportion of B-S- progeny will be 0.19, or 19%.

Question 16

The three genes,D,E,and F,are closely linked as indicated on the map below.In this region of the genome,there is no interference (the coefficient of coincidence is 1).

If a trihybrid with genotype ABC/abc is testcrossed,what is the expected percent of "parentals" within the progeny?
A)8.5%
B)15%
C)42.5%
D)85%
E)85.5%

Accepted Answer

The answer of The three genes,D,E,and F,are closely linked as...

Question 17

A plant of genotype C/C ^. d/d is crossed to c/c ^. D/D,and the F₁ is testcrossed.If the genes in question are linked,the percentage of double homozygous recessive individuals in the offspring of the testcross will be: A)less than 25%. B)about 25%. C)more than 25% but less than 50%. D)about 50%. E)more than 50% but less than 75%.

Accepted Answer

The genotype of the parent plant can be written as C/C d/d S1U1P1.S1S1P0/S1U1P1.S1S1P0. The genotype of the parent it is crossed with can be written as c/c D/D S1U1P1.S1S1P0/S1U1P1.S1S1P0. 
The F1 generation will have the genotype C/c D/d S1U1P1.S1S1P0/S1U1P1.S1S1P0, which is the result of the independent assortment of the genes. 
When the F1 generation is testcrossed with a double homozygous recessive individual (c/c d/d S1S1P0/S1S1P0), the possible gametes produced by the F1 are CD or Cd (from the D/d parent) and S1U1P1.S1S1P0 or S1S1P0 (from both parents). 
The possible offspring of the testcross are: 
- C/d S1U1P1.S1S1P0/S1S1P0 (16.67%)
- C/d S1U1P1.S1U1P1/S1S1P0 (16.67%)
- C/d S1U1P1.S1S1P0/S1U1P1 (16.67%)
- C/d S1U1P1.S1U1P1/S1U1P1 (16.67%)
- c/d S1U1P1.S1S1P0/S1S1P0 (16.67%)
- c/d S1U1P1.S1U1P1/S1S1P0 (16.67%)
- c/d S1U1P1.S1S1P0/S1U1P1 (16.67%)
- c/d S1U1P1.S1U1P1/S1U1P1 (16.67%)
None of these possible offspring are double homozygous recessive, therefore the percentage of double homozygous recessive individuals in the offspring of the testcross will be less than 25%.

Question 18

In maize,two plants that are both heterozygous for the recessive alleles a and b are crossed.What frequency of double-mutant progeny will appear if a and b are 7.2 map units apart,and both parents carry a and b in repulsion (trans)?
A)0.001296
B)0.005184
C)0.036
D)0.0625
E)0.072

Accepted Answer

The correct answer is A because the frequency of double-mutant progeny is 0.001296. This is because the two genes are 7.2 map units apart, and the parents are in repulsion (trans). This means that the genes are on opposite chromosomes, and the probability of recombination between them is 0.072. The probability of getting a double mutant is the product of the probabilities of getting a mutant at each gene, which is 0.072 * 0.072 = 0.001296.

Question 19

A plant of genotype C/C ;d/d is crossed to c/c ;D/D,and the F₁ is testcrossed.If the genes in question are unlinked,the percentage of double homozygous recessive individuals in the offspring of the testcross will be: A)less than 25%. B)about 25%. C)more than 25%,but less than 50%. D)about 50%. E)more than 50% but less than 75%.

Accepted Answer

The parental cross is C/C ;d/d x c/c ;D/D, which results in all heterozygous F1 offspring (C/c ; D/d). Testcrossing the F1 to a double homozygous recessive individual (c/c ; d/d) will result in four possible gametes from the F1: c/d, c/d, C/d, and C/d. Each of these gametes has an equal chance of combining with either c or d from the testcross parent. Therefore, the possible offspring genotypes and frequencies are:

c/c ; d/d = 25%
c/c ; D/d = 25%
C/c ; d/d = 25%
C/c ; D/d = 25%

Only the first genotype is double homozygous recessive, so the percentage of double homozygous recessive individuals in the testcross offspring is about 25%.

Question 20

In maize,the genes W and D are so tightly linked that virtually no crossovers occur between them.A dihybrid W d/w D is testcrossed to w d/w d.The percent of progeny with W-/D- phenotype will be:
A)0.
B)25.
C)50.
D)75.
E)100.

Accepted Answer

We know that the genes W and D are tightly linked, meaning they are located close together on the same chromosome. This makes it very unlikely for a crossover to occur between them during meiosis. Therefore, they will almost always be inherited together in the same gamete.

In the dihybrid individual W d/w D, the two dominant alleles (W and D) are located on the same chromosome, while the two recessive alleles (w and d) are on the other homologous chromosome. When this individual is testcrossed to a homozygous recessive individual (w d/w d), the gametes produced by the dihybrid individual will be W d and w D in equal proportions.

When we look at the resulting progeny, we see that there are four possible gamete combinations:

- W d/w d
- W D/w d
- w d/w d
- w D/w d

Of these four possibilities, only one (W d/w d) has the W and D alleles together, and therefore exhibits the W-/D- phenotype. Because this is only one out of four possible gamete combinations, the percentage of progeny with the W-/D- phenotype will be 25%, and not 0%, as there would be some recombinants due to chromosomal segregation.

Quiz 4: Mapping Eukaryote Chromosomes by Recombination

Out of 800 progeny of a three-point testcross,there were 16 double crossover recombinants,whereas 80 had been expected on the basis of no interference.The interference is:

The maize genes sh and bz are linked,40 map units apart.If a plant sh⁺bz/sh bz⁺ is selfed,what proportion of the progeny will be sh bz/sh bz?

A male mouse of genotype A/a ^. B/b is testcrossed multiple times.Overall,these testcrosses produce 11 mice of phenotype A B,81 A b,77 a B,and 14 a b.Based on these data,the genotypes of the male mouse's parents are most likely:

The F,G,and H loci are linked in the order written.There are 30 map units between F and G,and 30 map units between G and H.If a plant F G H/f g h is testcrossed,what proportion of progeny plants will be f g h/f g h if there is no interference?

The linkage relationships among the four mouse genes,A,B,C,and D,are shown in the map below. What proportion of the eggs produced by a female mouse with genotype Ab/aB;CD/cd will carry all the recessive alleles?

In an experimental plant,the genes t and q are linked.A pure breeding t/t individual is crossed to a pure breeding q/q individual to obtain a dihybrid F₁.Genotypically,the F₁individuals can be described as:

Two genes,A and B,are linked.An individual of genotype A b/A b is crossed to one that is a B/a B.The F₁ is selfed and an F₂ is obtained.Which of the following ratios most likely represents the phenotypic ratio observed in this F₂?

A dihybrid in cis is crossed to a dihybrid in trans (the two genes of interest,A and B,are linked) .What proportion of the progeny is expected to be homozygous recessive with respect to the two genes of interest?

Two genes,A and B,are linked.An individual of genotype A b/A b is crossed to one that is a B/a B.The F₁ is testcrossed.Which of the following ratios most likely represents the phenotypic ratio observed in the progeny of this testcross?

In Drosophila,the two genes w and sn are X-linked and 25 map units apart.A female fly of genotype w⁺sn⁺/w sn is crossed to a male from a wild-type line.What percent of male progeny will be w⁺sn?

The mouse autosomal genes B and S are linked and 38 map units apart.Genotypes B S/B S and b s/b s are intercrossed,and the F₁ is testcrossed to b s/b s.The proportion of B-S- progeny will be:

The three genes,D,E,and F,are closely linked as indicated on the map below.In this region of the genome,there is no interference (the coefficient of coincidence is 1) . If a trihybrid with genotype ABC/abc is testcrossed,what is the expected percent of "parentals" within the progeny?

A plant of genotype C/C ^. d/d is crossed to c/c ^. D/D,and the F₁ is testcrossed.If the genes in question are linked,the percentage of double homozygous recessive individuals in the offspring of the testcross will be:

In maize,two plants that are both heterozygous for the recessive alleles a and b are crossed.What frequency of double-mutant progeny will appear if a and b are 7.2 map units apart,and both parents carry a and b in repulsion (trans) ?

A plant of genotype C/C ;d/d is crossed to c/c ;D/D,and the F₁ is testcrossed.If the genes in question are unlinked,the percentage of double homozygous recessive individuals in the offspring of the testcross will be:

In maize,the genes W and D are so tightly linked that virtually no crossovers occur between them.A dihybrid W d/w D is testcrossed to w d/w d.The percent of progeny with W-/D- phenotype will be:

Quiz 4: Mapping Eukaryote Chromosomes by Recombination

Out of 800 progeny of a three-point testcross,there were 16 double crossover recombinants,whereas 80 had been expected on the basis of no interference.The interference is:

The maize genes sh and bz are linked,40 map units apart.If a plant sh+bz/sh bz+ is selfed,what proportion of the progeny will be sh bz/sh bz?

A male mouse of genotype A/a . B/b is testcrossed multiple times.Overall,these testcrosses produce 11 mice of phenotype A B,81 A b,77 a B,and 14 a b.Based on these data,the genotypes of the male mouse's parents are most likely:

The F,G,and H loci are linked in the order written.There are 30 map units between F and G,and 30 map units between G and H.If a plant F G H/f g h is testcrossed,what proportion of progeny plants will be f g h/f g h if there is no interference?

The linkage relationships among the four mouse genes,A,B,C,and D,are shown in the map below. What proportion of the eggs produced by a female mouse with genotype Ab/aB;CD/cd will carry all the recessive alleles?

In an experimental plant,the genes t and q are linked.A pure breeding t/t individual is crossed to a pure breeding q/q individual to obtain a dihybrid F1.Genotypically,the F1 individuals can be described as:

Two genes,A and B,are linked.An individual of genotype A b/A b is crossed to one that is a B/a B.The F1 is selfed and an F2 is obtained.Which of the following ratios most likely represents the phenotypic ratio observed in this F2?