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

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

Q: A Drosophila geneticist observes 0.5% recombination between yellow and white genes, and 34.5% between white and miniature. What is the distance between yellow and miniature genes?

$$0.5 + 34.5 = 35.0 \\ \text{mu}$$

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

A test cross is performed between an F1 dihybrid (hv+ bw+/hv bw) and a double recessive parent (hv bw/hv bw). If the genes are completely linked, what is the expected phenotypic ratio in the offspring?

Accepted Answer

1:1

Question 3

Which of the following best describes the outcome of crossing over between two homologous chromosomes during meiosis?

Accepted Answer

It increases genetic variation by producing recombinant chromosomes.

Question 4

If the recombination frequency between two genes is 12%, what is the distance between them on a chromosome map?

Accepted Answer

$$12 \ 	ext{mu}$$

Question 5

Which scientist first proposed that the frequency of recombinant offspring is proportional to the distance between genes on a chromosome?

Accepted Answer

Alfred Sturtevant

Question 6

In a three-point test cross involving genes y, w, and ec in Drosophila, the rarest phenotypic class represents which of the following?

Accepted Answer

Double crossover events

Question 7

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

Accepted Answer

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

Question 8

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

Accepted Answer

Sister chromatids are genetically identical, so exchanges do not create new allele combinations.

Question 9

A Drosophila geneticist observes 0.5% recombination between yellow and white genes, and 34.5% between white and miniature. What is the distance between yellow and miniature genes?

Accepted Answer

$$0.5 + 34.5 = 35.0 \ 	ext{mu}$$

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

In a dihybrid cross involving two genes on the same chromosome, which of the following ratios would indicate complete linkage in the F2 generation?

Accepted Answer

1:2:1

Question 12

Which of the following best describes a linkage group?

Accepted Answer

All genes located on the same chromosome

Question 13

A geneticist finds that the recombination frequency between two genes is 50%. What does this suggest about the genes?

Accepted Answer

They are either on different chromosomes or far apart on the same chromosome.

Question 14

Which of the following is true regarding the maximum observable recombination frequency between two genes?

Accepted Answer

It cannot exceed 50%.

Question 15

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

Accepted Answer

Formation of recombinant chromosomes

Question 16

A student calculates the probability of a double crossover between two gene pairs as $$0.06 \times 0.04. $$What is the probability, and what does this represent?

Accepted Answer

$$0.0024 or$$ $$0.24\%$$, representing the expected frequency of double crossovers

Question 17

Which of the following is NOT a plausible reason why mapping estimates become less accurate as the distance between genes increases?

Accepted Answer

Genes that are far apart always show complete linkage.

Question 18

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

Accepted Answer

Bloom syndrome

Question 19

Which of the following statements about single and double crossovers is correct?

Accepted Answer

Double crossovers are less frequent than single crossovers and require two separate crossover events.

Chromosome Mapping and Genetic Linkage in Eukaryotes

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