Question 1

Which of the following best describes the outcome when two genes are completely linked and no crossing over occurs during meiosis?

Accepted Answer

Only parental (noncrossover) gametes are produced.

Question 2

If two genes are located very close together on the same chromosome, what is the expected recombination frequency between them?

Accepted Answer

Close to 0%

Question 3

A testcross is performed between an individual heterozygous for two genes (AaBb) and a double homozygous recessive (aabb). If the genes are unlinked, what phenotypic ratio is expected in the offspring?

Accepted Answer

1:1:1:1

Question 4

Which of the following statements about chiasmata is correct?

Accepted Answer

Chiasmata are points of genetic exchange between nonsister chromatids during meiosis.

Question 5

Given the following recombination frequencies: yellow-white = 0.5%, white-miniature = 34.5%, yellow-miniature = 35.4%. What is the correct gene order on the chromosome?

Accepted Answer

yellow - white - miniature

Question 6

How many map units (centimorgans) apart are two genes if the recombination frequency between them is 12%?

Accepted Answer

$$12 \ 	ext{mu}$$

Question 7

If a single crossover occurs 100% of the time between two linked genes, what proportion of the gametes will be recombinant?

Accepted Answer

$$50\%$$

Question 8

Why did Gregor Mendel not observe linkage in his pea plant experiments?

Accepted Answer

The genes he studied were either on different chromosomes or so far apart on the same chromosome that linkage was not detected.

Question 9

Which of the following best explains why recombination frequencies between linked genes are additive?

Accepted Answer

Because the probability of crossing over between two genes includes all possible crossovers between them and any intervening genes.

Question 10

A heterozygote for two genes (Ab/aB) is testcrossed to a double mutant (ab/ab). If the genes are 10 map units apart, what proportion of the offspring will be recombinant?

Accepted Answer

$$0.20$$

Question 11

Which of the following is true regarding the effect of gene distance on crossing over?

Accepted Answer

The farther apart two genes are, the more likely crossing over will occur between them.

Question 12

In a cross between Ab/Ab and aB/aB, what is the genotype of the F1 generation if no crossing over occurs?

Accepted Answer

Ab/aB

Question 13

Which of the following best describes a map unit (centimorgan)?

Accepted Answer

A 1% recombination frequency between two genes.

Question 14

If two genes are 35.4 map units apart, what is the expected recombination frequency between them?

Accepted Answer

$$35.4\%$$

Question 15

Which of the following is a consequence of crossing over during meiosis?

Accepted Answer

It produces recombinant chromosomes.

Question 16

A single crossover event between two genes produces which of the following gamete types?

Accepted Answer

Both parental and recombinant gametes

Question 17

If the recombination frequency between two genes is 50%, what can you conclude about their genetic relationship?

Accepted Answer

They are unlinked or on different chromosomes.

Question 18

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

Accepted Answer

Because independent assortment produces equal numbers of parental and recombinant gametes.

Question 19

In a three-point testcross, the gene order is determined by comparing the frequency of double crossovers to single crossovers. Which gene is in the middle?

Accepted Answer

The gene that is exchanged in double crossover events.

CH5.1: Chromosome Mapping in Eukaryotes: Linkage, Crossing Over, and Genetic Mapping

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