Q: If the recombination frequency between gene A and gene B is $$28\%$$ and between gene B and gene C is $$17\%$$, what is the expected frequency of double crossovers between A and C?

$$0.28 \times 0.17 = 0.0476 or$$ $$4.76\%$$

Question 1

Which of the following statements best explains why genes located close together on the same chromosome tend to be inherited together?

Accepted Answer

They are less likely to be separated by crossing over due to their proximity.

Question 2

In a dihybrid cross involving two genes on the same chromosome with complete linkage, what phenotypic ratio would you expect in the F2 generation?

Accepted Answer

$$1:2:1$$

Question 3

If two genes are 10 map units apart, what percentage of the gametes produced by a heterozygote will be recombinant for these genes?

Accepted Answer

$$10\%$$

Question 4

A test cross is performed between an individual heterozygous for two completely linked genes and a homozygous recessive individual. What is the expected phenotypic ratio in the offspring?

Accepted Answer

$$1:1$$

Question 5

Which of the following best describes the significance of crossing over during meiosis?

Accepted Answer

It increases genetic variation by producing recombinant chromosomes.

Question 6

If the recombination frequency between gene A and gene B is $$28\%$$ and between gene B and gene C is $$17\%$$, what is the expected frequency of double crossovers between A and C?

Accepted Answer

$$0.28 	imes 0.17 = 0.0476 or$$ $$4.76\%$$

Question 7

Why do genetic exchanges between sister chromatids not result in new recombinant chromatids?

Accepted Answer

Because sister chromatids are genetically identical.

Question 8

Which scientist first suggested that the frequency of recombinant individuals is related to the distance between genes on a chromosome?

Accepted Answer

Thomas Hunt Morgan

Question 9

A three-point test cross in Drosophila yields the following recombination frequencies: $$y$$ and $$w$$: $$1.56\%$$, $$w$$ and $$ec$$: $$4.06\%. $$What is the total map distance between $$y$$ and $$ec$$?

Accepted Answer

$$1.56 + 4.06 = 5.62$$\,mu

Question 10

Which of the following is a modern technique used for chromosome mapping that does NOT rely on classical genetic crosses?

Accepted Answer

Microsatellite analysis

Question 11

If two genes are so far apart on a chromosome that crossing over occurs between them in every meiosis, what recombination frequency would you expect?

Accepted Answer

$$50\%$$

Question 12

Which of the following best describes a linkage group?

Accepted Answer

All genes located on the same chromosome

Question 13

A geneticist observes that the frequency of recombinant offspring between two genes is $$35\%. $$What is the approximate map distance between these genes?

Accepted Answer

$$35$$\,mu

Question 14

Which of the following is true about double crossovers (DCOs) in three-point mapping experiments?

Accepted Answer

They are less frequent than single crossovers.

Question 15

In a three-point test cross, which phenotype class is used to determine the gene order on the chromosome?

Accepted Answer

The least frequent class

Question 16

Which of the following best explains why mapping estimates become less accurate as the distance between genes increases?

Accepted Answer

Multiple crossovers can occur, which may not be detected.

Question 17

A chromosome map shows that gene X is 7.5 mu from gene Y, and gene Y is 11.8 mu from gene Z. What is the minimum possible map distance between gene X and gene Z?

Accepted Answer

$$7.5 + 11.8 = 19.3$$\,mu

Question 18

Which of the following is NOT a plausible outcome of a single crossover event between two non-sister chromatids during meiosis?

Accepted Answer

Production of only parental-type gametes

Question 19

Which of the following diseases is associated with increased sister chromatid exchanges (SCEs)?

Accepted Answer

Bloom syndrome

Chromosome Mapping and Genetic Linkage in Eukaryotes

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