Q: In a test cross between a dihybrid individual (AaBb) and a double recessive (aabb), the following offspring numbers are observed: 420 AaBb, 430 aabb, 75 Aabb, 75 aaBb. What is the recombination frequency between the two genes?

$$\frac{75 + 75}{420 + 430 + 75 + 75} \times 100 = 15\%$$

Question 1

Which of the following best describes Mendel's Law of Independent Assortment?

Accepted Answer

During gamete formation, the segregation of one pair of hereditary determinants is independent of the segregation of other pairs.

Question 2

If two genes are located on the same chromosome and are very close together, which of the following is most likely to be true?

Accepted Answer

They will be inherited together more often than not due to reduced likelihood of crossing over.

Question 3

A geneticist observes that two genes show a recombination frequency of 12%. What is the approximate map distance between these genes?

Accepted Answer

$$12 \ 	ext{map units}$$

Question 4

Which of the following statements about linked genes is FALSE?

Accepted Answer

Linked genes are always inherited independently.

Question 5

In a test cross between a dihybrid individual (AaBb) and a double recessive (aabb), the following offspring numbers are observed: 420 AaBb, 430 aabb, 75 Aabb, 75 aaBb. What is the recombination frequency between the two genes?

Accepted Answer

$$\frac{75 + 75}{420 + 430 + 75 + 75} 	imes 100 = 15\%$$

Question 6

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

Accepted Answer

Production of recombinant gametes with new allele combinations.

Question 7

Why do genes that are far apart on the same chromosome sometimes appear to assort independently?

Accepted Answer

Because crossing over occurs so frequently between them that recombinant gametes are produced at a rate similar to independent assortment.

Question 8

Which of the following best explains why recombination frequencies never exceed 50% between two genes?

Accepted Answer

At 50% recombination, genes assort as if they are on different chromosomes, indicating independent assortment.

Question 9

A plant breeder wants to map two genes and finds a recombination frequency of 1%. What does this indicate about the physical distance between the genes?

Accepted Answer

The genes are very close together on the chromosome.

Question 10

Which of the following is NOT a use of genetic maps in modern biology?

Accepted Answer

Determining the exact nucleotide sequence of a gene.

Question 11

In a cross involving two linked genes, the parental types are observed at a much higher frequency than the recombinant types. What does this suggest about the distance between the two genes?

Accepted Answer

The genes are close together on the chromosome.

Question 12

Which formula correctly calculates the map distance between two genes based on offspring counts?

Accepted Answer

$$	ext{Map distance (mu)} = \frac{	ext{Number of recombinant offspring}}{	ext{Total number of offspring}} 	imes 100$$

Question 13

Which of the following best describes a chiasma?

Accepted Answer

A point where homologous chromosomes exchange genetic material during meiosis.

Question 14

If two genes show 0% recombination in a test cross, what is the most likely explanation?

Accepted Answer

The genes are so close together on the same chromosome that crossing over between them is extremely rare or absent.

Question 15

A geneticist performs a cross and observes the following offspring: 542 parental type 1, 537 parental type 2, 76 recombinant type 1, 75 recombinant type 2. What is the map distance between the two genes?

Accepted Answer

$$\frac{76 + 75}{542 + 537 + 76 + 75} 	imes 100 = 12.3 \ 	ext{map units}$$

Question 16

Which of the following statements about crossing over is TRUE?

Accepted Answer

Crossing over increases the genetic diversity of gametes.

Question 17

Which of the following would be the expected result if two genes are completely linked and no crossing over occurs between them?

Accepted Answer

Only parental (non-recombinant) gametes will be produced.

Question 18

Why are genetic maps based on recombination frequencies not always perfectly accurate representations of physical distances between genes?

Accepted Answer

Because recombination frequency does not always increase linearly with physical distance, especially for genes far apart on the same chromosome.

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