Question 1

Which of the following best describes the physical relationship between genes and chromosomes?

Accepted Answer

Genes are segments of DNA located on chromosomes, which are structures made of DNA and proteins.

Question 2

Thomas Hunt Morgan’s experiments with Drosophila melanogaster provided the first solid evidence that:

Accepted Answer

Genes are located on chromosomes.

Question 3

In Morgan’s experiment, a cross between a wild-type female fruit fly and a white-eyed male resulted in all F1 offspring having red eyes. In the F2 generation, only males had white eyes. What does this pattern suggest?

Accepted Answer

The gene for eye color is located on the X chromosome.

Question 4

Which of the following statements about X-linked recessive disorders is correct?

Accepted Answer

Males are more likely to express X-linked recessive disorders because they have only one X chromosome.

Question 5

A female cat that is heterozygous for a fur color gene located on the X chromosome can have patches of both black and orange fur. This phenomenon is best explained by:

Accepted Answer

Random X chromosome inactivation in each cell during embryonic development.

Question 6

Which of the following best explains why linked genes do not always show perfect linkage in offspring phenotypes?

Accepted Answer

Crossing over during meiosis can separate linked genes, resulting in recombinant phenotypes.

Question 7

If two genes are located on different chromosomes, what is the expected frequency of recombination between them?

Accepted Answer

$$50\%$$

Question 8

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

Accepted Answer

$$XXY$$

Question 9

Which chromosomal abnormality results from the failure of homologous chromosomes to separate during meiosis?

Accepted Answer

Nondisjunction

Question 10

Down syndrome is caused by which specific chromosomal alteration?

Accepted Answer

Trisomy 21

Question 11

Which of the following is NOT a possible result of a chromosomal breakage?

Accepted Answer

Polyploidy

Question 12

A woman who is a carrier for an X-linked recessive disorder and a man who does not have the disorder have a son. What is the probability that their son will have the disorder?

Accepted Answer

$$50\%$$

Question 13

Which of the following best describes a Barr body?

Accepted Answer

An inactivated X chromosome in a female cell

Question 14

If a gamete receives two copies of the same chromosome due to nondisjunction, and is fertilized by a normal gamete, what is the resulting zygote called?

Accepted Answer

Trisomic

Question 15

Which of the following is a real-world example of a human condition caused by a chromosomal translocation?

Accepted Answer

Chronic myelogenous leukemia (CML)

Question 16

A geneticist observes that two genes show a recombination frequency of 10%. What does this indicate about their physical location?

Accepted Answer

The genes are close together on the same chromosome.

Question 17

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

Accepted Answer

Older eggs are more likely to undergo nondisjunction during meiosis.

Question 18

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

Accepted Answer

They are passed directly from father to son.

Question 19

A plant with genotype $$YyRr is $$testcrossed with a $$yyrr$$ plant. If the genes are unlinked, what proportion of the offspring will be recombinant types?

Accepted Answer

$$50\%$$

Question 20

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

Accepted Answer

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

The Chromosomal Basis of Inheritance

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