Question 1

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

Accepted Answer

Males are hemizygous for the X chromosome, so a single recessive allele on the X chromosome will be expressed.

Question 2

A woman who is heterozygous for the X-linked gene for colorblindness has children with a man who is not colorblind. What is the probability that their son will be colorblind?

Accepted Answer

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

Question 3

Which syndrome results from a human having a karyotype of 47 chromosomes, including two X chromosomes and one Y chromosome ($$XXY$$)?

Accepted Answer

Klinefelter syndrome

Question 4

If nondisjunction occurs during meiosis I in a human oocyte, what is the expected outcome for the resulting gametes?

Accepted Answer

All gametes will have an abnormal chromosome number.

Question 5

Which of the following statements about X inactivation in female mammals is correct?

Accepted Answer

One X chromosome is randomly inactivated in each cell during embryonic development.

Question 6

A gene is located on the Y chromosome. Which of the following statements is true about its inheritance?

Accepted Answer

It is passed directly from father to son.

Question 7

Which of the following best describes linked genes?

Accepted Answer

Genes located on the same chromosome that tend to be inherited together.

Question 8

A child is born with only one X chromosome and no second sex chromosome. Which condition does this describe?

Accepted Answer

Turner syndrome

Question 9

If two genes are located far apart on the same chromosome, their recombination frequency approaches which value?

Accepted Answer

$$50\%$$

Question 10

Which gene is responsible for determining maleness in humans?

Accepted Answer

SRY gene on the Y chromosome

Question 11

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

Accepted Answer

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

Question 12

Which of the following is an example of polyploidy?

Accepted Answer

A plant with four complete sets of chromosomes

Question 13

Genomic imprinting in mammals results in which of the following?

Accepted Answer

Certain genes are silenced depending on the parent of origin.

Question 14

Which of the following best describes a monosomic zygote?

Accepted Answer

It has only one copy of a particular chromosome.

Question 15

A healthy female with a karyotype of $$47,XXX is $$most likely to:

Accepted Answer

Be phenotypically normal with no unusual physical conditions.

Question 16

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

Accepted Answer

X-linked genes can be inherited from either parent.

Question 17

If a male inherits a recessive allele for hemophilia (an X-linked disorder) from his mother, what is the probability he will express the disorder?

Accepted Answer

$$1$$

Question 18

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

Accepted Answer

Males have one X and one Y chromosome.

Question 19

Which of the following is true about genes located on the X chromosome?

Accepted Answer

They can affect traits unrelated to gender.

Question 20

If nondisjunction occurs during meiosis II, what is the expected distribution of normal and abnormal gametes?

Accepted Answer

Two normal gametes and two abnormal gametes.

Chromosomal Basis of Inheritance and Sex Determination

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