Question 1

Which of the following best describes a map unit (mu) in chromosome mapping?

Accepted Answer

A relative distance corresponding to 1% recombination frequency between two genes.

Question 2

If the recombination frequency between gene A and gene B is 20%, and between gene B and gene C is 30%, what is the expected frequency of double-crossover gametes between A and C?

Accepted Answer

$$20\% 	imes 30\% = 6\%$$

Question 3

In a three-point test cross, which class of offspring is expected to occur at the lowest frequency?

Accepted Answer

Double-crossover class

Question 4

Which of the following is a requirement for a successful three-point mapping cross?

Accepted Answer

The cross must be constructed so the genotypes of all gametes can be determined by observing the phenotype of the offspring.

Question 5

If the observed frequency of double crossovers is less than the expected frequency, what type of interference is present?

Accepted Answer

Positive interference

Question 6

Given the following recombination frequencies: $$y-w = 0.5 mu$$, $$w-ec = 34.5 mu$$, $$y-ec = 35.4 mu$$, which gene is in the middle?

Accepted Answer

w

Question 7

Which of the following statements about double crossovers (DCOs) is correct?

Accepted Answer

DCOs can be used to determine the order of three genes on a chromosome.

Question 8

In a mapping experiment, the expected DCO frequency between two genes is $$9.7\%$$, but the observed DCO frequency is $$7.8\%. $$What is the coefficient of coincidence?

Accepted Answer

$$\frac{7.8\%}{9.7\%} = 0.80$$

Question 9

Which of the following best explains why mapping accuracy decreases as the distance between two genes increases?

Accepted Answer

Multiple crossovers between distant genes may not be detected, leading to underestimation of the true distance.

Question 10

Which experimental approach allows researchers to assign genes to specific human chromosomes using hybrid cell lines?

Accepted Answer

Synteny testing

Question 11

If two genes are 60 map units apart, what is the expected recombination frequency between them?

Accepted Answer

$$50\%$$

Question 12

Which of the following is true regarding the product law in genetics?

Accepted Answer

It is used to calculate the probability of two independent crossover events occurring simultaneously.

Question 13

In a three-point cross, how can you determine which gene is in the middle?

Accepted Answer

By identifying the gene that is switched in the double-crossover phenotype compared to the noncrossover phenotype.

Question 14

Which of the following is a consequence of positive interference in genetic mapping?

Accepted Answer

Fewer double crossovers are observed than expected.

Question 15

A researcher observes that the phenotypic classes of offspring representing double crossovers occur less frequently than single crossover classes. What does this indicate?

Accepted Answer

Double crossovers are less likely than single crossovers.

Question 16

Which of the following statements about somatic cell hybridization is correct?

Accepted Answer

It involves the fusion of two cells to form a hybrid cell, which can be used to assign genes to specific chromosomes.

Question 17

Which of the following best describes the relationship between recombination frequency and physical distance on a chromosome?

Accepted Answer

Recombination frequency provides a relative, not absolute, measure of physical distance.

Question 18

In a three-point cross, the distance between genes v and pr is calculated by adding the frequency of single crossovers between v and pr and the frequency of double crossovers. If the SCO frequency is $$14.5\%$$ and the DCO frequency is $$7.8\%$$, what is the map distance?

Accepted Answer

$$14.5\% + 7.8\% = 22.3 mu$$

Question 19

Which of the following is a reason why two genes that are far apart on a chromosome may show a recombination frequency of only 50%?

Accepted Answer

Multiple crossovers between the genes can restore the parental arrangement, making them appear unlinked.

Chromosome Mapping in Eukaryotes: Principles and Applications

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