Question 1

Which of the following best explains why Drosophila melanogaster (fruit flies) were an ideal organism for Thomas Hunt Morgan's genetic experiments?

Accepted Answer

They produce many offspring, have a short generation time, and possess only four pairs of chromosomes.

Question 2

A male with Klinefelter syndrome has which of the following sex chromosome compositions?

Accepted Answer

$$XXY$$

Question 3

Which of the following statements about the law of independent assortment is correct?

Accepted Answer

It applies only to genes located on different chromosomes or far apart on the same chromosome.

Question 4

A woman who is heterozygous for an X-linked recessive disorder and a man who is unaffected have a son. What is the probability that their son will be affected by the disorder?

Accepted Answer

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

Question 5

Which chromosomal abnormality is most likely to result in Down syndrome?

Accepted Answer

Trisomy 21

Question 6

If a female mammal is heterozygous for a gene on the X chromosome, what is the expected result in her somatic cells due to X inactivation?

Accepted Answer

Some cells will express the dominant allele and others the recessive allele, resulting in a mosaic pattern.

Question 7

A testcross between a dihybrid Drosophila (gray body, normal wings) and a double mutant (black body, vestigial wings) produces mostly parental-type offspring and fewer recombinants. What does this indicate about the genes for body color and wing shape?

Accepted Answer

They are located close together on the same chromosome (linked genes).

Question 8

Which of the following best describes the genetic event known as nondisjunction?

Accepted Answer

Homologous chromosomes or sister chromatids fail to separate during meiosis.

Question 9

A child is born with cri du chat syndrome. Which chromosomal alteration is responsible for this disorder?

Accepted Answer

Deletion on chromosome 5

Question 10

Which of the following is true about polyploidy?

Accepted Answer

It results in organisms with more than two complete sets of chromosomes.

Question 11

A male inherits an X-linked recessive allele from his mother. Which of the following is true?

Accepted Answer

He will always express the trait associated with the allele.

Question 12

Which of the following chromosomal changes is most likely to result in the Philadelphia chromosome, associated with chronic myelogenous leukemia (CML)?

Accepted Answer

Translocation

Question 13

If a gene is located on the Y chromosome, which of the following statements is correct?

Accepted Answer

It is only passed from father to son.

Question 14

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

Accepted Answer

$$XO$$

Question 15

Which of the following best explains why the frequency of Down syndrome increases with maternal age?

Accepted Answer

Older mothers have a higher rate of nondisjunction during meiosis.

Question 16

In a dihybrid cross involving two genes on different chromosomes, what is the expected phenotypic ratio in the F2 generation?

Accepted Answer

$$9:3:3:1$$

Question 17

Which of the following is a real-life example of a disorder caused by a chromosomal deletion?

Accepted Answer

Cri du chat syndrome

Question 18

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

Accepted Answer

Random X chromosome inactivation in different cells.

Question 19

Which of the following best describes the result of a reciprocal translocation?

Accepted Answer

A segment of a chromosome is moved to a nonhomologous chromosome.

Question 20

If a cell has three copies of every chromosome, what is its ploidy level?

Accepted Answer

$$3n$$

The Chromosomal Basis of Inheritance

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