Q: If the recombination frequency between gene A and B is 0.10 and between B and C is 0.20, what is the expected frequency of double crossover gametes in a trihybrid cross (assuming no interference)?

$$(0.10) \times (0.20) = 0.02 or$$ $$2\%$$

Q: Which of the following is a correct formula for calculating recombination frequency ($$r$$)?

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

Question 1

Which of the following statements best describes genetic linkage?

Accepted Answer

Genes located on the same chromosome that are always inherited together due to their physical proximity.

Question 2

If two genes are 10 map units apart, what is the expected frequency of recombinant gametes produced by a dihybrid individual?

Accepted Answer

$$0.10 or$$ $$10\%$$

Question 3

In a test cross between AaBb (where A and B are linked) and aabb, the following progeny numbers are observed: 400 AaBb, 400 aabb, 100 Aabb, 100 aaBb. What is the recombination frequency ($$r) $$between A and B?

Accepted Answer

$$r = \frac{100 + 100}{400 + 400 + 100 + 100} = \frac{200}{1000} = 0.20$$

Question 4

Which of the following best explains why parental allele combinations are observed more frequently than recombinant combinations in linked genes?

Accepted Answer

Linked genes are so close together that crossing over between them is rare.

Question 5

What is the unit of genetic distance used in linkage mapping, and how is it defined?

Accepted Answer

Centimorgan (cM); 1 cM = 1\% recombination frequency

Question 6

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

Accepted Answer

Double crossover recombinants

Question 7

If the recombination frequency between gene A and B is 0.10 and between B and C is 0.20, what is the expected frequency of double crossover gametes in a trihybrid cross (assuming no interference)?

Accepted Answer

$$(0.10) 	imes (0.20) = 0.02 or$$ $$2\%$$

Question 8

Which experimental result would indicate that two genes are completely linked?

Accepted Answer

Only parental phenotypes are observed in the progeny.

Question 9

Why did Bateson and Punnett observe more parental phenotypes than expected in their F2 sweet pea cross?

Accepted Answer

The genes for flower color and pollen shape were linked and did not assort independently.

Question 10

In a dihybrid test cross involving unlinked genes, what is the expected phenotypic ratio among the progeny?

Accepted Answer

1:1:1:1

Question 11

Which of the following best describes the effect of gene distance on recombination frequency?

Accepted Answer

The farther apart two genes are, the higher the recombination frequency.

Question 12

A chi-square test is performed on the progeny of a genetic cross and yields a p-value less than 0.05. What does this indicate about the genes being tested?

Accepted Answer

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

Question 13

Which of the following is a correct formula for calculating recombination frequency ($$r$$)?

Accepted Answer

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

Question 14

In a three-point test cross, how can you determine which gene is in the middle?

Accepted Answer

Compare the parental and double-crossover progeny; the gene that differs is in the middle.

Question 15

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

Accepted Answer

Interference

Question 16

Which of the following is true about the relationship between physical and genetic maps?

Accepted Answer

Genetic maps are based on recombination frequencies, while physical maps are based on actual DNA sequence distances.

Question 17

A dihybrid organism with genotype AaBb (genes 10 cM apart) produces gametes. What proportion of its gametes will be AB?

Accepted Answer

$$0.45 or$$ $$45\%$$

Question 18

Which of the following best describes the outcome of a cross between a trihybrid (ABC/abc) and a homozygous recessive (abc/abc) when A-B is 10 cM and B-C is 20 cM apart, assuming no interference?

Accepted Answer

The most frequent gametes will be parental types (ABC and abc), and the least frequent will be double recombinants (AbC and aBc).

Genetic Linkage and Mapping in Eukaryotes

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