Q: Which equation correctly expresses recombination frequency ($$r) $$between two genes?

$$r = \frac{\text{number of recombinants}}{\text{total number of progeny}}$$

Question 1

Which of the following statements best describes syntenic genes?

Accepted Answer

Genes located on the same chromosome.

Question 2

In a dihybrid cross involving linked genes A and B, which gamete combinations will occur at a frequency greater than 50%?

Accepted Answer

Parental gametes (AB and ab)

Question 3

Which equation correctly expresses recombination frequency ($$r) $$between two genes?

Accepted Answer

$$r = \frac{	ext{number of recombinants}}{	ext{total number of progeny}}$$

Question 4

Why do closely linked genes exhibit lower recombination frequencies than genes that are farther apart?

Accepted Answer

Because crossing over is less likely to occur between closely linked genes.

Question 5

In a test cross between a dihybrid (AaBb) and a homozygous recessive (aabb), what would you expect if the genes are unlinked?

Accepted Answer

Four types of progeny in equal proportions.

Question 6

Which organism is known to exhibit complete genetic linkage due to the absence of crossing over?

Accepted Answer

Drosophila males

Question 7

A geneticist observes significantly more parental phenotypes than recombinant phenotypes in a cross. What does this suggest about the genes involved?

Accepted Answer

The genes are linked and located near each other on the same chromosome.

Question 8

If two genes are 10 map units apart, what is the expected frequency of recombinant gametes for each recombinant type?

Accepted Answer

$$0.05$$

Question 9

Which historical experiment provided direct cytological evidence that recombination is accompanied by physical exchange between homologous chromosomes?

Accepted Answer

Creighton and McClintock's corn experiment.

Question 10

In a three-point test cross, which class of gametes is expected to be the least frequent?

Accepted Answer

Double-crossover gametes

Question 11

If the observed number of double crossovers in a three-point test cross is less than expected, what phenomenon does this illustrate?

Accepted Answer

Positive interference

Question 12

Given the following recombination frequencies: $$r_{AB} = 0.10$$ and $$r_{BC} = 0.20$$, what is the expected frequency of double-crossover gametes in a trihybrid cross?

Accepted Answer

$$0.02$$

Question 13

Which of the following best explains why genetic map distances can underestimate the physical distance between two genes?

Accepted Answer

Double crossovers between a pair of genes may not be detected in the progeny phenotype.

Question 14

In a three-point test cross, how can the gene order be determined using double-crossover progeny?

Accepted Answer

By comparing parental and double-crossover genotypes; the gene that differs is in the middle.

Question 15

What is the coefficient of coincidence ($$c) if $$the observed number of double crossovers is 11 and the expected is 18.2?

Accepted Answer

$$c = \frac{11}{18.2} = 0.60$$

Question 16

Which of the following is true regarding the relationship between recombination frequency and gene distance?

Accepted Answer

Genes that are farther apart have higher recombination frequencies.

Question 17

A geneticist performs a chi-square test on progeny data and obtains a p-value \u003c 0.005. What does this indicate about the genes being studied?

Accepted Answer

There is a significant deviation from independent assortment, suggesting genetic linkage.

Question 18

In a trihybrid cross (A B C / a b c) where A-B is 10 cM and B-C is 20 cM apart, what is the expected frequency of gametes with no crossover in either interval?

Accepted Answer

$$(1-0.10) 	imes (1-0.20) = 0.72$$

Question 19

Which of the following best describes the phenomenon of 'coupling' as proposed by Bateson and Punnett?

Accepted Answer

An unknown mechanism that keeps parental gamete combinations together.

5. Genetic Linkage and Mapping in Eukaryotes

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