Q: A testcross AaBb x aabb produces the following progeny: 10 AaBb, 40 aaBb, 40 Aabb, and 10 aabb. What is the percent recombination between the A and B loci?

$$\frac{10 + 10}{100} \times 100 = 20\%$$

Q: Which of the following is a correct formula for calculating recombination frequency?

$$\text{Recombination Frequency} = \frac{\text{Number of recombinant progeny}}{\text{Total number of progeny}} \times 100$$

Question 1

Which of the following statements best describes the difference between linked and unlinked genes?

Accepted Answer

Linked genes are located on the same chromosome and tend to be inherited together, while unlinked genes are on different chromosomes and assort independently.

Question 2

A testcross AaBb x aabb produces the following progeny: 10 AaBb, 40 aaBb, 40 Aabb, and 10 aabb. What is the percent recombination between the A and B loci?

Accepted Answer

$$\frac{10 + 10}{100} 	imes 100 = 20\%$$

Question 3

In a dihybrid testcross (AaBb x aabb), what progeny ratio would you expect if the genes are unlinked?

Accepted Answer

1:1:1:1

Question 4

Which experimental result provided direct evidence that crossing over involves a physical exchange between homologous chromosomes?

Accepted Answer

Barbara McClintock and Harriet Creighton's maize chromosome 9 experiment

Question 5

If two genes are 16 map units apart, what percentage of the gametes produced by a heterozygote will be recombinant for these genes?

Accepted Answer

16\%

Question 6

Which of the following best explains why the maximum observed recombination frequency between two genes is 50\%?

Accepted Answer

At 50\% recombination, genes assort independently, as if they are on different chromosomes.

Question 7

A three-point testcross produces the following progeny numbers: 82, 70, 21, 21, 17, 13, 4, 2. Which step should you perform first to determine gene order?

Accepted Answer

Identify the parental and double crossover classes.

Question 8

In a three-point testcross, the observed number of double crossovers is 8, and the expected number is 13.4. What is the coefficient of coincidence?

Accepted Answer

$$\frac{8}{13.4} = 0.60$$

Question 9

Which of the following is a correct formula for calculating recombination frequency?

Accepted Answer

$$	ext{Recombination Frequency} = \frac{	ext{Number of recombinant progeny}}{	ext{Total number of progeny}} 	imes 100$$

Question 10

A geneticist observes that the recombination frequency between genes b and c is 20\%, between b and d is 10\%, and between c and d is 28\%. What is the most likely explanation for why the c-d distance is less than the sum of b-c and b-d?

Accepted Answer

Double crossovers reduce the observed number of recombinant progeny.

Question 11

In a deletion mapping experiment, if a gene of interest is within the deleted region, what phenotype ratio is expected in the progeny?

Accepted Answer

Half of the progeny will display the mutant phenotype.

Question 12

Which of the following best describes the effect of interference in genetic mapping?

Accepted Answer

One crossover event reduces the probability of another crossover occurring nearby.

Question 13

A pedigree shows that all children with nail-patella syndrome also have blood type B or O, but not A. What does this suggest about the genes for nail-patella syndrome and blood type?

Accepted Answer

The genes are linked on the same chromosome.

Question 14

Which of the following is true about the coupling (cis) and repulsion (trans) configurations of linked genes?

Accepted Answer

The configuration does not affect the recombination frequency.

Question 15

If the interference value is 0.2, what does this indicate about crossover events?

Accepted Answer

20\% of expected double crossovers did not occur due to interference.

Question 16

Which of the following is a real-world application of gene mapping in humans?

Accepted Answer

Using pedigrees to determine the chromosomal location of disease genes.

Question 17

In a two-point testcross, you observe 16 recombinant progeny and 84 nonrecombinant progeny. What is the map distance between the two genes?

Accepted Answer

$$\frac{16}{100} 	imes 100 = 16$$ map units

Question 18

Which of the following best describes the relationship between recombination frequency and actual map distance as shown in the provided graph?

Accepted Answer

Recombination frequency increases with map distance but never exceeds 50\%.

Linkage, Recombination, and Eukaryotic Gene Mapping

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