Question 1

Which of the following best explains why X-linked recessive disorders are more common in males than in females?

Accepted Answer

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

Question 2

A woman who is heterozygous for the X-linked gene for color blindness (XᴺXⁿ) has children with a man who is not color blind (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 chromosome.

Question 4

A geneticist observes a recombination frequency of 9% between two genes in fruit flies. What does this indicate about the genes’ locations?

Accepted Answer

The genes are close together on the same chromosome.

Question 5

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

Accepted Answer

Some gametes have an extra chromosome, and some are missing a chromosome.

Question 6

Down syndrome is caused by which chromosomal abnormality?

Accepted Answer

Trisomy of chromosome 21

Question 7

A female cat is heterozygous for a gene on the X chromosome that determines fur color. Due to X inactivation, what is the expected phenotype?

Accepted Answer

The cat will be a mosaic, showing patches of both fur colors.

Question 8

Which of the following best describes the chromosomal basis of gender in humans?

Accepted Answer

Females are XX and males are XY.

Question 9

If two genes are 17 map units apart on a chromosome, what is the expected recombination frequency between them?

Accepted Answer

$$17\%$$

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

Accepted Answer

A deletion on chromosome 5

Question 12

Which syndrome is the only known viable monosomy in humans?

Accepted Answer

Turner syndrome

Question 13

Which of the following statements about genomic imprinting is correct?

Accepted Answer

It involves the silencing of certain genes depending on the parent of origin.

Question 14

A woman with mitochondrial myopathy marries a healthy man. What is the probability that their children will inherit the disorder?

Accepted Answer

All of their children

Question 15

Which of the following best explains why genes that are far apart on the same chromosome can have a recombination frequency near 50%?

Accepted Answer

They are physically linked but genetically unlinked due to frequent crossing over.

Question 16

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

Accepted Answer

XXY

Question 17

Which process is responsible for the production of recombinant chromosomes during meiosis?

Accepted Answer

Crossing over

Question 18

A geneticist is mapping three genes (A, B, and C) on a chromosome. The recombination frequency between A and B is 9%, between B and C is 9.5%, and between A and C is 17%. What is the most likely order of these genes?

Accepted Answer

A - B - C

Question 19

Which of the following is an example of a disorder caused by a chromosomal translocation?

Accepted Answer

Chronic myelogenous leukemia (CML)

Question 20

Which of the following best describes the inheritance of extranuclear genes?

Accepted Answer

They are inherited only from the mother.

The Chromosomal Basis of Inheritance

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