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

A large sample size to recover all crossover classes.

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 map distances: $$y-w = 0.5 mu$$, $$w-m = 34.5 mu$$, and $$y-m = 35.4 mu$$, which gene is in the middle?

Accepted Answer

w

Question 7

Why does the accuracy of genetic mapping decrease as the distance between two genes increases?

Accepted Answer

Because multiple crossovers between distant genes may not be detected.

Question 8

In a three-point cross, how is the gene order determined using double crossover (DCO) phenotypes?

Accepted Answer

By identifying the gene that is switched relative to the noncrossover arrangement.

Question 9

If the expected frequency of double crossovers is $$9.7\%$$ and the observed frequency is $$7.8\%$$, what is the coefficient of coincidence?

Accepted Answer

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

Question 10

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 is then used for 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 best explains why double crossovers are less frequent than single crossovers?

Accepted Answer

Double crossovers require two independent crossover events to occur simultaneously.

Question 13

In a three-point cross, the distance between two genes is calculated by:

Accepted Answer

Adding the percentage of single crossovers and double crossovers between them.

Question 14

Which of the following is true about reciprocal classes of phenotypes in a three-point cross?

Accepted Answer

They complement each other, with one being wild type and the other mutant for all three genes.

Question 15

Synteny testing allows researchers to:

Accepted Answer

Assign genes to specific chromosomes.

Question 16

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

Accepted Answer

Fewer double crossovers than expected are observed.

Question 17

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

Accepted Answer

Recombination frequency is a relative measure, while physical distance is measured in base pairs.

Question 18

In a mapping experiment, why might the observed number of recombinant offspring be lower than expected for genes that are far apart?

Accepted Answer

Because double crossovers restore the parental arrangement, making some recombinants undetectable.

Question 19

Which of the following is NOT a criterion for a successful three-point mapping cross?

Accepted Answer

The parent must be homozygous for all three genes.

CH5.2: Chromosome Mapping in Eukaryotes: Principles and Applications

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