Q: A testcross between a dihybrid fruit fly (b+ b vg+ vg) and a double mutant (b b vg vg) produces 965 gray-normal, 944 black-vestigial, 206 gray-vestigial, and 185 black-normal offspring. What is the recombination frequency between the b and vg genes?

$$\frac{206 + 185}{965 + 944 + 206 + 185} \times 100 = 17\%$$

Question 1

Which of the following best explains why Morgan chose Drosophila melanogaster (fruit flies) for his genetic experiments?

Accepted Answer

They have only four pairs of chromosomes and a short generation time, making them ideal for genetic studies.

Question 2

A woman who is heterozygous for the X-linked gene for color blindness (XᴺXⁿ) marries a man with normal vision (XᴺY). What is the probability that their son will be color blind?

Accepted Answer

$$\frac{1}{2}$$

Question 3

Which chromosomal alteration is correctly matched with its description?

Accepted Answer

Inversion: A segment of a chromosome is reversed within the same chromosome.

Question 4

A geneticist observes a 9:3:3:1 phenotypic ratio in the F2 generation of a dihybrid cross. Which Mendelian law does this observation support?

Accepted Answer

Law of Independent Assortment

Question 5

Which of the following is a consequence of nondisjunction during meiosis?

Accepted Answer

Some gametes have an extra chromosome, while others are missing one.

Question 6

A child is born with cri du chat syndrome. Which chromosomal event most likely caused this disorder?

Accepted Answer

A deletion on chromosome 5

Question 7

Which of the following best describes the genetic makeup of an individual with Klinefelter syndrome?

Accepted Answer

$$XXY$$

Question 8

If a female cat is heterozygous for the X-linked gene controlling fur color, what is the expected phenotype and why?

Accepted Answer

She will be a mosaic (patchy) for fur color because different X chromosomes are inactivated in different cells.

Question 9

Which of the following is true about linked genes?

Accepted Answer

They are located on the same chromosome and tend to be inherited together.

Question 10

A testcross between a dihybrid fruit fly (b+ b vg+ vg) and a double mutant (b b vg vg) produces 965 gray-normal, 944 black-vestigial, 206 gray-vestigial, and 185 black-normal offspring. What is the recombination frequency between the b and vg genes?

Accepted Answer

$$\frac{206 + 185}{965 + 944 + 206 + 185} 	imes 100 = 17\%$$

Question 11

Which of the following best explains why Down syndrome is more common in children born to older mothers?

Accepted Answer

Older mothers are more likely to experience nondisjunction during meiosis.

Question 12

Which of the following is an example of polyploidy?

Accepted Answer

A plant with four complete sets of chromosomes ($$4n)$$

Question 13

Which of the following statements about the SRY gene is correct?

Accepted Answer

It is located on the Y chromosome and triggers male development.

Question 14

A male inherits an X-linked recessive disorder from his mother. Which of the following best explains why males are more likely to express X-linked recessive disorders?

Accepted Answer

Males have only one X chromosome, so a single recessive allele will cause the disorder.

Question 15

Which chromosomal event is associated with chronic myelogenous leukemia (CML)?

Accepted Answer

A reciprocal translocation between chromosomes 9 and 22

Question 16

Which of the following best describes the difference between aneuploidy and polyploidy?

Accepted Answer

Aneuploidy is the presence of extra or missing individual chromosomes, while polyploidy is the presence of extra sets of chromosomes.

Question 17

Which of the following is a possible outcome of X chromosome inactivation in female mammals?

Accepted Answer

One X chromosome is randomly inactivated in each cell, leading to mosaic expression of X-linked genes.

Question 18

Which of the following best describes the law of segregation?

Accepted Answer

The two alleles for a gene separate during gamete formation.

Question 19

A woman with Turner syndrome has which of the following karyotypes?

Accepted Answer

$$X0$$

Question 20

Which of the following is true about the inheritance of Y-linked genes?

Accepted Answer

They are passed from fathers to all of their sons.

The Chromosomal Basis of Inheritance

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