Question 1

Which of the following best explains why genes that are 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

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

Accepted Answer

$$10\%$$

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 crossing over is correct?

Accepted Answer

Crossing over increases genetic variability by producing recombinant chromosomes.

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

If a single crossover occurs 100% of the time between two linked genes, what is the maximum recombination frequency observed?

Accepted Answer

$$50\%$$

Question 7

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 8

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

Accepted Answer

The percentage of recombinant offspring produced by crossing over between two genes.

Question 9

In a cross between Ab/Ab and aB/aB individuals, assuming complete linkage and no crossing over, what genotypes are expected in the F1 generation?

Accepted Answer

Ab/aB

Question 10

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

Accepted Answer

$$1:1:1:1$$

Question 11

Which of the following is a direct consequence of chiasmata formation during meiosis?

Accepted Answer

Exchange of genetic material between nonsister chromatids

Question 12

A single crossover event between two genes on a chromosome will result in which of the following?

Accepted Answer

Two recombinant and two parental gametes are produced, but only two chromatids are involved in the crossover.

Question 13

If the recombination frequency between two genes is $$35\%$$, how many map units apart are they?

Accepted Answer

$$35$$ map units$

Question 14

Which of the following crosses would produce a 1:2:1 phenotypic ratio in the F2 generation if the genes are completely linked?

Accepted Answer

Ab/Ab x aB/aB followed by F1 self-cross

Question 15

Which of the following best describes the relationship between recombination frequency and physical distance between genes?

Accepted Answer

Recombination frequency increases as physical distance increases.

Question 16

If two genes are completely linked, what types of gametes will be produced by a heterozygote?

Accepted Answer

Only parental (noncrossover) gametes

Question 17

Which of the following is NOT a reason why Mendel did not detect linkage in his experiments?

Accepted Answer

He did not study enough traits.

Question 18

Which of the following is true regarding the additive nature of recombination frequencies?

Accepted Answer

The recombination frequency between two distant genes is the sum of the frequencies between intermediate genes.

Question 19

A geneticist observes that two genes show a recombination frequency of $$0.5\%. $$What does this suggest about their physical relationship?

Accepted Answer

They are very close together on the same chromosome.

Question 20

Which of the following best describes the outcome of a double crossover event between three genes on a chromosome?

Accepted Answer

It can produce double-crossover gametes that differ from both parental and single-crossover types.

Chromosome Mapping in Eukaryotes: Linkage, Recombination, and Genetic Mapping

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