Question 1

The cross Lpq / lPQ * lpq / lpq is carried out and the L gene is found to be in the middle.What would be the genotypes of the double crossover gametes in this cross?

Accepted Answer

The double crossover gametes would have the genotype LPQ and lpq because the L gene is in the middle.

Question 2

The map of a chromosome interval is: A--10 mu--B--40 mu--C
From the cross Abc / aBC * abc / abc, how many double crossovers would be expected out of 1000 progeny?

Accepted Answer

The answer of The map of a chromosome interval is:...

Question 3

Suppose a three-point testcross was conducted involving the genes X, Y, and Z.If the most abundant classes are XYz and xyZ and the rarest classes are xYZ and Xyz, which gene is in the middle?

Accepted Answer

The answer of Suppose a three-point testcross was conducted involving...

Question 4

In tetrad analysis, NPD asci result from

Accepted Answer

NPD (non-parental ditype) asci can result from either independent assortment of unlinked genes or from double crossovers between linked genes, as both scenarios can produce non-parental combinations of alleles.

Question 5

The zipper-like connection between paired homologs in early prophase is known as a

Accepted Answer

The zipper-like connection between paired homologs in early prophase is known as the synaptonemal complex. It helps to align and connect the homologs, allowing for crossing over and genetic exchange.

Question 6

In tetrad analysis, the criterion for linkage of two genes is

Accepted Answer

PD > NPDIn tetrad analysis, the criterion for linkage of two genes is PD > NPD. This is because if two genes are linked, then they will tend to be inherited together more often than would be expected by chance. This will result in a higher proportion of parental ditype (PD) tetrads than non-parental ditype (NPD) tetrads.

Question 7

In Drosophila, the genes y (yellow body) and car (carnation eyes) are located at opposite ends of the X chromosome.In doubly heterozygous females (y⁺ car⁺/ y car), a single chiasma is observed somewhere along the X chromosome in 90% of the examined oocytes.No X chromosomes with multiple chiasmata are observed.What percentage of the male progeny from such a female would be recombinant for y and car?

Accepted Answer

The answer of In Drosophila, the genes y (yellow body)...

Question 8

In tetrad analysis, second-division segregations result from

Accepted Answer

Second-division segregations occur when a crossover event happens between a gene and the centromere, causing the alleles to segregate into different nuclei during the second meiotic division.

Question 9

Genes Q and R are 20 map units apart.If a plant of genotype QR / qr is selfed, what percentage of the progeny will be qr in phenotype?

Accepted Answer

The answer of Genes Q and R are 20 map...

Question 10

A dihybrid test cross is made between genes H and I.Four categories of offspring are produced: HI, Hi, hI, and hi.You wish to use the $ \chi$² test to test the hypothesis that the H and I genes are unlinked.How many degrees of freedom would there be in this test?

Accepted Answer

The answer of A dihybrid test cross is made between...

Question 11

In Drosophila, the genes b, c, and sp are linked and arranged as shown below: b--30 mu--c--20 mu--sp
This region exhibits 90% interference.How many double crossovers would be recovered in a three-point cross involving b, c, and sp out of 1000 progeny?

Accepted Answer

Interference is the phenomenon where the occurrence of a crossover in one region of a chromosome inhibits the occurrence of another crossover nearby. With 90% interference, only 10% of the expected double crossovers occur. The expected double crossovers without considering interference can be calculated by multiplying the individual crossover frequencies: (30 m.u. * 20 m.u.) / 100^2 = 0.06 or 6%. Out of 1000 progeny, 6% would be 60. However, with 90% interference, only 10% of these 60 double crossovers are expected to occur, resulting in 6 double crossovers (60 * 0.1 = 6).

Question 12

Tetrad analysis shows that crossing over occurs at the four-strand stage (i.e., after replication) because, when two genes are linked,

Accepted Answer

T (tetratype) > NPD (non-parental ditype) indicates crossing-over between linked genes, as tetratypes result from single crossover events between two genes, showing that recombination occurs after DNA replication in the four-strand stage.

Question 13

Which of the following processes can generate recombinant gametes?

Accepted Answer

Crossing over between two linked heterozygous loci can result in the exchange of genetic material between homologous chromosomes, generating new combinations of alleles in gametes. Independent assortment of two unlinked heterozygous loci can also generate new combinations of alleles in gametes. Both of these processes are present in choice D. Segregation of alleles in a heterozygote can also occur, but it is not sufficient to generate recombinant gametes on its own. Choice E includes all three processes, but it is not necessary to include segregation of alleles in a heterozygote along with the other two processes to generate recombinant gametes.

Question 14

The R/r and S/s genes are linked and 10 map units apart.In the cross Rs / rS * rs / rs what percentage of the progeny will be Rs / rs?

Accepted Answer

The answer of The R/r and S/s genes are linked...

Question 15

The measured distance between genes D and E in a two point test cross is 50 map units.What does this mean in physical terms?

Accepted Answer

A distance of 50 map units suggests either the genes are on different chromosomes or they are linked but far enough apart that they assort independently, appearing as if they are on different chromosomes.

Question 16

Suppose an individual is heterozygous for a pair of alleles (e.g., A/a).Under what conditions would a crossover in a somatic cell of this individual lead to a clone of cells homozygous for a? (Pick the most precise answer.)

Accepted Answer

In order for a clone of cells to be homozygous for a particular allele, the crossover must occur within the region between the locus and the centromere, involving two homologous (non-sister) chromatids. This allows for a recombinant chromosome that has lost the other allele and contains two copies of the allele of interest. Crossovers that occur on the same chromosome arm but not in this specific region may still result in recombinant chromosomes, but they will not result in the loss or gain of alleles that lead to homozygosity. Sister chromatids are identical copies and do not undergo crossing over. Crossovers between the locus and the end of the chromosome may or may not result in homozygosity, depending on whether the resulting recombinant chromosome is lost or retained during subsequent cell division.

Question 17

The Q gene locus is 10 map units from the R gene locus which is 40 map units from the S gene locus: Q--10 mu--R--40 mu--S
Which interval would likely show the higher ratio of double to single chiasmata?

Accepted Answer

The higher ratio of double to single chiasmata occurs in the interval with the longest distance, which is R-S in this case. The longer the distance between the loci, the higher the probability of double crossovers occurring within the interval. Q-R is a shorter interval, so it would have a lower ratio of double to single chiasmata. Option C, that the ratios would be the same in both intervals, is incorrect because the distance between the loci affects the frequency of double crossovers. Option D, that two chiasmata never occur in the same interval, is incorrect because double crossovers can and do occur within an interval.

Question 18

Recombination frequencies near 50% suggest that

Accepted Answer

Recombination frequency is a measure of the distance between two genes. If the recombination frequency is near 50%, it suggests that the two genes are either on different chromosomes or on the same chromosome but very far apart. Therefore, choice D is the best answer. The other choices are less likely because if the genes were on different chromosomes, the recombination frequency would be close to 0%, and if the genes were very close together on the same chromosome, the recombination frequency would be close to 0% or 100%.

Question 19

Crossing over takes place in paired bivalents consisting of ______ chromatids, and involves _______ of the chromatids.

Accepted Answer

The answer of Crossing over takes place in paired bivalents...

Question 20

Sturtevant's detailed mapping studies of the X chromosome of Drosophila established what genetic principle?

Accepted Answer

Sturtevant's mapping studies of the X chromosome of Drosophila established the linear arrangement of genes on chromosomes. This principle, known as linkage, allowed for the prediction of the relative distance between genes on a chromosome and paved the way for the development of genetic mapping.

Quiz 5: Linkage, Recombination, and the Mapping of Genes on Chromosomes

The cross Lpq / lPQ * lpq / lpq is carried out and the L gene is found to be in the middle.What would be the genotypes of the double crossover gametes in this cross?

The map of a chromosome interval is: A--10 mu--B--40 mu--C From the cross Abc / aBC * abc / abc, how many double crossovers would be expected out of 1000 progeny?

Suppose a three-point testcross was conducted involving the genes X, Y, and Z.If the most abundant classes are XYz and xyZ and the rarest classes are xYZ and Xyz, which gene is in the middle?

In tetrad analysis, NPD asci result from

The zipper-like connection between paired homologs in early prophase is known as a

In tetrad analysis, the criterion for linkage of two genes is

In tetrad analysis, second-division segregations result from

Genes Q and R are 20 map units apart.If a plant of genotype QR / qr is selfed, what percentage of the progeny will be qr in phenotype?

A dihybrid test cross is made between genes H and I.Four categories of offspring are produced: HI, Hi, hI, and hi.You wish to use the $\chi$ ² test to test the hypothesis that the H and I genes are unlinked.How many degrees of freedom would there be in this test?

In Drosophila, the genes b, c, and sp are linked and arranged as shown below: b--30 mu--c--20 mu--sp This region exhibits 90% interference.How many double crossovers would be recovered in a three-point cross involving b, c, and sp out of 1000 progeny?

Tetrad analysis shows that crossing over occurs at the four-strand stage (i.e., after replication) because, when two genes are linked,

Which of the following processes can generate recombinant gametes?

The R/r and S/s genes are linked and 10 map units apart.In the cross Rs / rS * rs / rs what percentage of the progeny will be Rs / rs?

The measured distance between genes D and E in a two point test cross is 50 map units.What does this mean in physical terms?

Suppose an individual is heterozygous for a pair of alleles (e.g., A/a) .Under what conditions would a crossover in a somatic cell of this individual lead to a clone of cells homozygous for a? (Pick the most precise answer.)

The Q gene locus is 10 map units from the R gene locus which is 40 map units from the S gene locus: Q--10 mu--R--40 mu--S Which interval would likely show the higher ratio of double to single chiasmata?

Recombination frequencies near 50% suggest that

Crossing over takes place in paired bivalents consisting of chromatids, and involves _ of the chromatids.

Sturtevant's detailed mapping studies of the X chromosome of Drosophila established what genetic principle?

Quiz 5: Linkage, Recombination, and the Mapping of Genes on Chromosomes

The cross Lpq / lPQ * lpq / lpq is carried out and the L gene is found to be in the middle.What would be the genotypes of the double crossover gametes in this cross?

The map of a chromosome interval is: A--10 mu--B--40 mu--C From the cross Abc / aBC * abc / abc, how many double crossovers would be expected out of 1000 progeny?

Suppose a three-point testcross was conducted involving the genes X, Y, and Z.If the most abundant classes are XYz and xyZ and the rarest classes are xYZ and Xyz, which gene is in the middle?

In tetrad analysis, NPD asci result from

The zipper-like connection between paired homologs in early prophase is known as a

In tetrad analysis, the criterion for linkage of two genes is

In tetrad analysis, second-division segregations result from

Genes Q and R are 20 map units apart.If a plant of genotype QR / qr is selfed, what percentage of the progeny will be qr in phenotype?

A dihybrid test cross is made between genes H and I.Four categories of offspring are produced: HI, Hi, hI, and hi.You wish to use the χ \chiχ 2 test to test the hypothesis that the H and I genes are unlinked.How many degrees of freedom would there be in this test?

In Drosophila, the genes b, c, and sp are linked and arranged as shown below: b--30 mu--c--20 mu--sp This region exhibits 90% interference.How many double crossovers would be recovered in a three-point cross involving b, c, and sp out of 1000 progeny?

Tetrad analysis shows that crossing over occurs at the four-strand stage (i.e., after replication) because, when two genes are linked,

Which of the following processes can generate recombinant gametes?

The R/r and S/s genes are linked and 10 map units apart.In the cross Rs / rS * rs / rs what percentage of the progeny will be Rs / rs?

The measured distance between genes D and E in a two point test cross is 50 map units.What does this mean in physical terms?

Suppose an individual is heterozygous for a pair of alleles (e.g., A/a) .Under what conditions would a crossover in a somatic cell of this individual lead to a clone of cells homozygous for a? (Pick the most precise answer.)

The Q gene locus is 10 map units from the R gene locus which is 40 map units from the S gene locus: Q--10 mu--R--40 mu--S Which interval would likely show the higher ratio of double to single chiasmata?

Recombination frequencies near 50% suggest that

Crossing over takes place in paired bivalents consisting of ______ chromatids, and involves _______ of the chromatids.

Sturtevant's detailed mapping studies of the X chromosome of Drosophila established what genetic principle?

A dihybrid test cross is made between genes H and I.Four categories of offspring are produced: HI, Hi, hI, and hi.You wish to use the $\chi$ ² test to test the hypothesis that the H and I genes are unlinked.How many degrees of freedom would there be in this test?

Crossing over takes place in paired bivalents consisting of chromatids, and involves _ of the chromatids.