Question 1

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

Accepted Answer

They are physically linked and less likely to be separated by crossing over.

Question 2

In a dihybrid cross between two heterozygotes for genes A and B (AaBb x AaBb), what phenotypic ratio would you expect in the F2 generation if the genes assort independently?

Accepted Answer

$$9:3:3:1$$

Question 3

If two genes are 16 map units apart, how many recombinant offspring would you expect in a mapping cross that produces 500 total offspring?

Accepted Answer

80

Question 4

Which of the following statements about recombination frequency is TRUE?

Accepted Answer

It provides information about the relative proximity of genes on a chromosome.

Question 5

A testcross is performed between an individual with genotype $$AB/ab$$ and a homozygous recessive $$ab/ab. If $$the genes are unlinked, what proportion of the offspring will be $$Ab/ab$$?

Accepted Answer

$$1/4$$

Question 6

Why is the maximum observable recombination frequency between two genes 50%?

Accepted Answer

Because at 50% recombination, genes assort as if they are on different chromosomes.

Question 7

In a cross between $$AaBb$$ and $$aabb$$, the following offspring are observed: $$AaBb = 40$$, $$Aabb = 10$$, $$aaBb = 10$$, $$aabb = 40. $$What is the recombination frequency between the two genes?

Accepted Answer

$$20\%$$

Question 8

Which of the following is a consequence of mitotic recombination in an organism?

Accepted Answer

It can result in patches of tissue with different phenotypes (twin spots).

Question 9

If the recombination frequency between genes A and B is 20%, and between B and C is 15%, what is the most likely order of these genes on the chromosome if the recombination frequency between A and C is 5%?

Accepted Answer

A - C - B

Question 10

A female Drosophila with genotype $$pr^+ vg^+ / pr vg is $$testcrossed with a $$pr vg$$ male. The following offspring are observed: $$pr^+ vg^+ (1339$$), $$pr vg (1195$$), $$pr^+ vg (151$$), $$pr vg^+ (154). $$What is the recombination frequency between the purple and vestigial genes?

Accepted Answer

$$10.7\%$$

Question 11

Which of the following best describes a linkage group?

Accepted Answer

A group of genes located on the same chromosome.

Question 12

In a testcross, what evidence would suggest that two genes are linked?

Accepted Answer

The majority of offspring have parental phenotypes, with fewer recombinants.

Question 13

Which stage of meiosis is primarily responsible for the physical process of crossing over?

Accepted Answer

Prophase I

Question 14

If two genes are so far apart on the same chromosome that crossing over always occurs between them, what is the expected phenotypic ratio in a testcross?

Accepted Answer

$$1:1:1:1$$

Question 15

A double crossover event between two genes will:

Accepted Answer

Sometimes restore the parental configuration, leading to underestimation of map distance.

Question 16

Which of the following is NOT a reason why recombination frequency may underestimate the true physical distance between two genes?

Accepted Answer

Recombination frequency is always equal to the physical distance.

Question 17

In a cross between $$DE/de$$ individuals where the genes are 20 map units apart, what proportion of gametes will be recombinant?

Accepted Answer

$$20\%$$

Question 18

Which of the following is a real-world example of mitotic recombination in humans?

Accepted Answer

Loss of heterozygosity in retinoblastoma.

Question 19

If the recombination frequency between genes R and S is 12%, and you cross $$Rs/rS$$ with $$rs/rs$$, what proportion of the progeny will be $$RS/rs$$?

Accepted Answer

$$0.06$$

Question 20

Which of the following statements about crossing over is FALSE?

Accepted Answer

It only occurs during mitosis.

Linkage and Chromosome Mapping in Eukaryotes: Study Notes for Genetics Students

Study Guide - Practice Questions

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