Q: A testcross between a dihybrid Drosophila (b extsuperscript{+}b vg extsuperscript{+}vg) and a double mutant (bb vgvg) produces 965 gray-normal, 944 black-vestigial, 206 gray-vestigial, and 185 black-normal offspring. What is the recombination frequency between the body color and wing shape 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 a short generation time and only four pairs of chromosomes, making them ideal for genetic studies.

Question 2

A woman who is heterozygous for the X-linked allele for color blindness (X	extsuperscript{N}X	extsuperscript{n}) marries a man with normal vision (X	extsuperscript{N}Y). What is the probability that their son will be color blind?

Accepted Answer

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

Question 3

Which chromosomal alteration is most likely to result in a child with cri du chat syndrome?

Accepted Answer

Deletion of a segment on chromosome 5

Question 4

If a male has an extra X chromosome (XXY), which syndrome does he have and what is a likely consequence?

Accepted Answer

Klinefelter syndrome; he will be sterile and may have some female body characteristics.

Question 5

Which of the following best describes the law of independent assortment?

Accepted Answer

Alleles of genes on nonhomologous chromosomes assort independently during gamete formation.

Question 6

A testcross between a dihybrid Drosophila (b	extsuperscript{+}b vg	extsuperscript{+}vg) and a double mutant (bb vgvg) produces 965 gray-normal, 944 black-vestigial, 206 gray-vestigial, and 185 black-normal offspring. What is the recombination frequency between the body color and wing shape genes?

Accepted Answer

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

Question 7

Which of the following is true about X chromosome inactivation in female mammals?

Accepted Answer

One X chromosome is randomly inactivated in each cell, forming a Barr body.

Question 8

A child is born with three copies of chromosome 21. Which of the following statements is correct?

Accepted Answer

This is an example of aneuploidy, specifically trisomy 21 (Down syndrome).

Question 9

Which of the following best explains why linked genes do not assort independently?

Accepted Answer

They are located close together on the same chromosome.

Question 10

A male with the genotype X	extsuperscript{n}Y for an X-linked recessive disorder and a female carrier (X	extsuperscript{N}X	extsuperscript{n}) have children. What is the probability that a daughter will be affected by the disorder?

Accepted Answer

$$\frac{1}{4}$$

Question 11

Which chromosomal event is most likely to result in chronic myelogenous leukemia (CML)?

Accepted Answer

A reciprocal translocation between chromosomes 9 and 22

Question 12

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

Accepted Answer

Some gametes have an abnormal number of chromosomes, leading to aneuploidy.

Question 13

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

Accepted Answer

Aneuploidy is the presence of an abnormal number of a particular chromosome, while polyploidy is the presence of more than two complete sets of chromosomes.

Question 14

Which of the following is NOT a possible result of a structural alteration of a chromosome?

Accepted Answer

Replication

Question 15

A female cat is heterozygous for the fur color gene located on the X chromosome. What is the most likely explanation for her patchy fur coloration?

Accepted Answer

Random X chromosome inactivation leads to a mosaic pattern of fur color.

Question 16

Which of the following best describes the function of the SRY gene?

Accepted Answer

It is responsible for the development of testes in males.

Question 17

If a plant species is tetraploid, how many sets of chromosomes does it have?

Accepted Answer

$$4n$$

Question 18

Which of the following is a likely outcome if nondisjunction occurs during meiosis II?

Accepted Answer

Half of the gametes will be normal, one will have an extra chromosome, and one will be missing a chromosome.

Question 19

Which of the following statements about Y-linked genes is correct?

Accepted Answer

They are passed from father to all of his sons.

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