Question 1

In corn, small pollen (sp)is recessive to normal pollen (sp⁺)and banded necrotic tissue, called zebra necrotic (zn), is recessive to normal tissue (zn⁺).The genes that produce these phenotypes are closely linked on chromosome 10.If no crossing over occurs between these two loci, give the types of progeny expected from the following cross:

Accepted Answer

The answer of In corn, small pollen (sp)is recessive to...

Question 2

Two genes, A and B, are located 30 map units apart.The dihybrid shown below is mated to a tester aa bb.What proportion of the offspring is expected to be dominant for both traits?

Accepted Answer

The answer of Two genes, A and B, are located...

Question 3

In flower beetles, pygmy (py)is recessive to normal size (py⁺), and red color (r)is recessive to brown (r⁺).A beetle heterozygous for these characteristics was test crossed to a beetle homozygous for pygmy and red.The following are progeny phenotypes from this testcross: Carry out a series of chi-square tests to determine if there is equal segregation of alleles at the py locus.What is the CORRECT chi-square value and how many degree(s)of freedom should be used in its interpretation?

Accepted Answer

The answer of In flower beetles, pygmy (py)is recessive to...

Question 4

Interference occurs when:

Accepted Answer

Interference occurs when one crossover event inhibits the occurrence of another crossover event nearby on the same chromosome, affecting the expected distribution of genetic recombinants.

Question 5

The map distances for genes that are close to each other are more accurate than map distances for genes that are quite far apart because:

Accepted Answer

With genes that are far apart, there is a higher chance of double crossover and other multiple crossover events occurring. These events often lead to nonrecombinant or parental offspring, which reduces the true map distance.

Question 6

In soreflies (a hypothetical insect), the dominant allele, L, is responsible for resistance to a common insecticide called Loritol.Another dominant allele, M, is responsible for the ability of soreflies to sing like birds.A true-breeding mute, Loritol-resistant sorefly was mated to a true-breeding singing, Loritol-sensitive sorefly, and the singing, Loritol-resistant female progeny were test-crossed with true-breeding wild-type (i.e., mute, Loritol-sensitive)males.Of the 400 total progeny produced, 117 were mute and Loritol-resistant, 114 could sing and were Loritol-sensitive, 83 could sing and were Loritol-resistant, and 86 were mute and Loritol-sensitive.What will be the results of a chi-square test for independent assortment?

Accepted Answer

The answer of In soreflies (a hypothetical insect), the dominant...

Question 7

You are studying two linked genes in lizards.You have two females and you know that both are the same genotype, heterozygous for both genes (A/a and B/b).You test-cross each female to a male that is fully homozygous recessive for both genes (a/a and b/b)and get the following progeny with the following phenotypes:  How can you explain the drastic difference between these two crosses?

Accepted Answer

The answer of You are studying two linked genes in...

Question 8

A low coefficient of coincidence indicates that:

Accepted Answer

A low coefficient of coincidence indicates that fewer double crossover recombinant progeny were recovered from a testcross than would be expected from the map distances of the genes involved. This suggests that the two genes are physically closer together on the chromosome than their genetic map distance would suggest, and that there is interference between crossovers.

Question 9

Three-factor testcrosses are only informative in gene mapping when which of the following occurs?

Accepted Answer

Three-factor testcrosses are most informative for gene mapping when one parent is heterozygous for the three genes (carrying both alleles for each gene) and the other parent is homozygous recessive (carrying two copies of the recessive allele for each gene). This setup allows for the observation of how the alleles segregate and recombine, providing information on the genes' relative locations and distances from each other on the chromosome.

Question 10

In soreflies (a hypothetical insect), the dominant allele, L, is responsible for resistance to a common insecticide called Loritol.Another dominant allele, M, is responsible for the ability of soreflies to sing like birds.A true-breeding mute, Loritol-resistant sorefly was mated to a true-breeding singing, Loritol-sensitive sorefly, and the singing, Loritol-resistant female progeny were test-crossed with true-breeding wild type (i.e., mute, Loritol-sensitive)males.Of the 400 total progeny produced, 117 were mute and Loritol-resistant, 114 could sing and were Loritol-sensitive, 83 could sing and were Loritol-resistant, and 86 were mute and Loritol-sensitive.A chi-square test is done to determine if there is equal segregation of alleles at the L locus.What will be the chi-square value obtained and how many degrees of freedom would be used to interpret this value?

Accepted Answer

The answer of In soreflies (a hypothetical insect), the dominant...

Question 11

Assume that A and B are two linked genes on an autosome in Drosophila.A testcross is made where AB/ab flies are crossed to ab/ab flies and the progeny are counted and shown below.However, it is known that the Aa/bb genotype is lethal before the flies hatch and does not appear among the testcross progeny counted.What is the most precise map distance that can be calculated from these data? Aa Bb = 235
Aa bb = 225
Aa Bb = 20

Accepted Answer

The answer of Assume that A and B are two...

Question 12

You are examining the following human pedigree and want to determine if the rare dominant disease allele (D)is linked to a specific DNA sequence location, referred to as a "molecular marker." You are using two molecular markers, R1 and R2.Parental and progeny genotypes and phenotypes are indicated.Note that the father is a dihybrid at both loci, but the mother is homozygous recessive at both loci and linked to R1 (d-R1/d-R1).There is complete penetrance of the trait and a linkage phase of D-R1/d-R2 in the father.Assuming that the marker and the gene are linked, what is the best estimate of the map distance between the two loci?

Accepted Answer

The answer of You are examining the following human pedigree...

Question 13

In flower beetles, pygmy (py)is recessive to normal size (py⁺), and red color (r)is recessive to brown (r⁺).A beetle heterozygous for these characteristics was test crossed to a beetle homozygous for pygmy and red.The following are progeny phenotypes from this testcross: Carry out a series of chi-square tests to determine if the two loci are assorting independently.What is the CORRECT chi-square value and how many degree(s)of freedom should be used in its interpretation?

Accepted Answer

The answer of In flower beetles, pygmy (py)is recessive to...

Question 14

An individual has the following genotype.Gene loci (A)and (B)are 15 cM apart.What are the CORRECT frequencies of some of the gametes that can be made by this individual?

Accepted Answer

The answer of An individual has the following genotype.Gene loci...

Question 15

Why are the progeny of a testcross generally used to map loci? Why not the F₂ progeny from an F₁ × F₁ cross?

Accepted Answer

The progeny of a testcross can be more easily classified into parental and recombinant categories because the tester parent is homozygous recessive for all alleles, whereas the F₁ × F₁ cross would result in a mixture of homozygous dominant, heterozygous, and homozygous recessive offspring.

Question 16

If the recombination frequency between genes (A)and (B)is 5.3%, what is the distance between the genes in map units on the linkage map?

Accepted Answer

The distance between genes on a linkage map is directly proportional to the recombination frequency between them. A recombination frequency of 5.3% translates directly to 5.3 centiMorgans (cM) on the linkage map.

Question 17

You just bought two black guinea pigs, one male and one female, of the same genotype from the pet store that are known to be heterozygous (Bb).You also know that black fur (BB)is dominant over white fur (bb)and that a lethal recessive allele is located only one cM away from the recessive b allele, and your animals are both heterozygous for this gene also.What is the probability of finding a white individual among the progeny if you cross these two animals?

Accepted Answer

The probability of obtaining a white (bb) guinea pig from two heterozygous (Bb) parents is 1/4 or 0.25 under simple Mendelian inheritance. However, because the lethal recessive allele is closely linked to the b allele (1 cM or 1% recombination frequency), the actual probability of a bb offspring surviving is reduced. The calculation for a surviving white (bb) individual takes into account the recombination frequency: 0.25 (chance of bb) * 0.99 (chance of not inheriting the lethal allele due to recombination) = 0.2475 or 0.004975 when expressed as a proportion of all possible outcomes, including those affected by the lethal allele.

Question 18

A series of two-point crosses among fruit flies is carried out between genes for brown eyes (bw), arc wings (a), vestigial wings (vg), ebony body color (e), and curved wings (cv).The following number of nonrecombinant and recombinant progeny were obtained from each cross:  Using these data from two-point crosses, what it the BEST genetic map (in cM)that can be developed?

Accepted Answer

The answer of A series of two-point crosses among fruit...

Question 19

Two linked genes, (A)and (B), are separated by 18 cM.A man with genotype Aa Bb marries a woman who is aa bb.The man's father was AA BB.What is the probability that their first two children will both be ab/ab?

Accepted Answer

The correct answer is A.The probability of the first child being ab/ab is 0.084. The probability of the second child being ab/ab is also 0.084. The probability of both children being ab/ab is 0.084 * 0.084 = 0.007056.

Question 20

You just bought two black guinea pigs, one male and one female, of the same genotype from the pet store that are known to be heterozygous (Bb).You also know that black fur (BB)is dominant over white fur (bb), and that a lethal recessive allele is located only one cM away from the recessive b allele and your animals are both heterozygous for this gene also.You decide to start raising your own guinea pigs, but after mating these animals several times, you discover they produce only black offspring among the first 12 progeny.How would you BEST explain this result?

Accepted Answer

The fact that the recessive lethal allele is located close to the b allele means that they are in tight coupling linkage. This means that almost all of the bb offspring will also be ll and thus die before they can be observed. Therefore, only black offspring will be observed, even though white offspring would be expected in a normal Mendelian ratio.

Quiz 5: Linkage, Recombination, and Eukaryotic Gene Mapping

Two genes, A and B, are located 30 map units apart.The dihybrid shown below is mated to a tester aa bb.What proportion of the offspring is expected to be dominant for both traits?

Interference occurs when:

The map distances for genes that are close to each other are more accurate than map distances for genes that are quite far apart because:

A low coefficient of coincidence indicates that:

Three-factor testcrosses are only informative in gene mapping when which of the following occurs?

An individual has the following genotype.Gene loci (A) and (B) are 15 cM apart.What are the CORRECT frequencies of some of the gametes that can be made by this individual?

Why are the progeny of a testcross generally used to map loci? Why not the F₂ progeny from an F₁ × F₁ cross?

If the recombination frequency between genes (A) and (B) is 5.3%, what is the distance between the genes in map units on the linkage map?

Two linked genes, (A) and (B) , are separated by 18 cM.A man with genotype Aa Bb marries a woman who is aa bb.The man's father was AA BB.What is the probability that their first two children will both be ab/ab?

Quiz 5: Linkage, Recombination, and Eukaryotic Gene Mapping

Two genes, A and B, are located 30 map units apart.The dihybrid shown below is mated to a tester aa bb.What proportion of the offspring is expected to be dominant for both traits?

Interference occurs when:

The map distances for genes that are close to each other are more accurate than map distances for genes that are quite far apart because:

A low coefficient of coincidence indicates that:

Three-factor testcrosses are only informative in gene mapping when which of the following occurs?

An individual has the following genotype.Gene loci (A) and (B) are 15 cM apart.What are the CORRECT frequencies of some of the gametes that can be made by this individual?

Why are the progeny of a testcross generally used to map loci? Why not the F2 progeny from an F1 × F1 cross?

If the recombination frequency between genes (A) and (B) is 5.3%, what is the distance between the genes in map units on the linkage map?

Two linked genes, (A) and (B) , are separated by 18 cM.A man with genotype Aa Bb marries a woman who is aa bb.The man's father was AA BB.What is the probability that their first two children will both be ab/ab?

Why are the progeny of a testcross generally used to map loci? Why not the F₂ progeny from an F₁ × F₁ cross?