Question 1

Which of the following best explains why sex-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 a carrier for hemophilia (an X-linked recessive disorder) has children with a man who has normal blood clotting. What is the probability that a son will have hemophilia?

Accepted Answer

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

Question 3

Which chromosomal alteration is most likely to result in a syndrome characterized by a missing chromosome, such as Turner syndrome?

Accepted Answer

Monosomy

Question 4

In Morgan’s experiments with Drosophila, what evidence supported the chromosomal theory of inheritance?

Accepted Answer

The inheritance of eye color was correlated with the sex of the offspring.

Question 5

If two genes are located far apart on the same chromosome, what is the expected recombination frequency between them?

Accepted Answer

$$50\%$$

Question 6

A genetic defect in humans results in the absence of sweat glands in the skin. In women, this defect is expressed in patches. What is the best explanation for this pattern?

Accepted Answer

X chromosome inactivation

Question 7

Which of the following chromosomal alterations is associated with the formation of a Philadelphia chromosome in chronic myelogenous leukemia?

Accepted Answer

Reciprocal translocation

Question 8

During meiosis, what event is responsible for the independent assortment of genes located on different chromosomes?

Accepted Answer

Random alignment of homologous chromosomes during metaphase I

Question 9

A testcross between an F1 dihybrid (AaBb) and a double recessive (aabb) produces offspring in a 1:1:1:1 ratio. What does this indicate about the genes?

Accepted Answer

The genes are unlinked and assort independently.

Question 10

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

Accepted Answer

Aneuploidy

Question 11

A woman with genotype $$X^D X^d ($$where $$X^D is $$the dominant normal allele and $$X^d is $$the recessive disease allele) has children with a man with genotype $$X^D Y. $$What fraction of their daughters will be carriers?

Accepted Answer

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

Question 12

Which chromosomal alteration is most likely to result in a genetic disorder due to the loss of several genes, such as Williams syndrome?

Accepted Answer

Deletion

Question 13

If a male inherits an X-linked recessive allele from his mother, what is the probability that he will express the trait?

Accepted Answer

$$1$$

Question 14

Which of the following best describes the effect of crossing over between homologous chromosomes?

Accepted Answer

It increases genetic variation by producing recombinant chromosomes.

Question 15

A person with Klinefelter syndrome has which of the following karyotypes?

Accepted Answer

XXY

Question 16

Which of the following is true about the X chromosome compared to the Y chromosome in humans?

Accepted Answer

The X chromosome contains many more genes than the Y chromosome.

Question 17

In a testcross involving two genes, you observe a recombination frequency of 17%. What does this indicate about the physical distance between the genes?

Accepted Answer

The genes are moderately far apart on the same chromosome.

Question 18

Which of the following chromosomal alterations is most likely to result in a healthy individual who may have reproductive difficulties due to improper chromosome pairing during meiosis?

Accepted Answer

Inversion

Question 19

A woman with normal vision and a man with normal vision have a son who is color-blind (an X-linked recessive trait). What are the genotypes of the parents?

Accepted Answer

Mother: $$X^N X^n$$, Father: $$X^N Y$$

Question 20

Which of the following best describes the outcome of a reciprocal translocation between two non-homologous chromosomes?

Accepted Answer

Exchange of segments between two non-homologous chromosomes, often with no immediate health effects but possible reproductive issues.

The Chromosomal Basis of Inheritance: Study Notes

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