Question 1

In humans, which gene is primarily responsible for initiating male sex determination, and what is its main function?

Accepted Answer

The SRY gene, which encodes a protein that triggers the development of testes from the embryonic gonad.

Question 2

A woman with normal color vision and a man who is color blind (X-linked recessive) have a son. What is the probability that their son will be color blind?

Accepted Answer

$$0\% ($$since the son inherits his X chromosome from his mother, who is not a carrier)

Question 3

Which of the following best describes the inheritance pattern of Y-linked (holandric) traits in humans?

Accepted Answer

They are inherited from father to all sons and never to daughters.

Question 4

A female carrier for hemophilia (an X-linked recessive disorder) and a normal male have a child. What is the probability that their daughter will have hemophilia?

Accepted Answer

$$0\% ($$since daughters would need two affected X chromosomes, and the father is normal)

Question 5

Which of the following statements about dosage compensation in mammals is correct?

Accepted Answer

Dosage compensation is achieved by inactivating one X chromosome in females, forming a Barr body.

Question 6

In birds, which sex is the heterogametic sex and what is their sex chromosome composition?

Accepted Answer

Females; $$ZW$$

Question 7

A geneticist observes a criss-cross inheritance pattern in a pedigree. Which type of inheritance is most likely being observed?

Accepted Answer

X-linked recessive

Question 8

Which of the following is true regarding the pseudoautosomal regions (PARs) of the human sex chromosomes?

Accepted Answer

PARs contain genes that follow autosomal patterns of inheritance.

Question 9

A male patient has an XY karyotype but develops as a phenotypic female with streak gonads and no secondary sexual characteristics. Which genetic condition best explains this scenario?

Accepted Answer

Swyer syndrome (XY gonadal dysgenesis) due to SRY gene mutation

Question 10

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 will be expressed.

Question 11

Which of the following is an example of a sex-limited trait in humans?

Accepted Answer

Beard growth

Question 12

In Drosophila, what is the mechanism of dosage compensation for X-linked genes?

Accepted Answer

Doubling the transcription of the single X chromosome in males

Question 13

A man with pattern baldness (sex-influenced trait, dominant in males, recessive in females) and a woman without baldness (homozygous non-bald) have a daughter. What is the probability that their daughter will be bald?

Accepted Answer

$$0\%$$

Question 14

Which gene is responsible for X-inactivation in mammals, and what is its product?

Accepted Answer

XIST gene; produces a long non-coding RNA that coats and silences the X chromosome

Question 15

Which of the following best describes the sex determination system in bees, wasps, and ants?

Accepted Answer

Females are diploid, males are haploid

Question 16

A geneticist is studying a trait that appears only in males, is passed from father to all sons, and never appears in females. Which type of inheritance is this?

Accepted Answer

Y-linked (holandric)

Question 17

Which of the following is a key difference between sex-limited and sex-influenced traits?

Accepted Answer

Sex-limited traits are only expressed in one sex, while sex-influenced traits can be expressed in both sexes but with different phenotypic effects.

Question 18

Which of the following scenarios would most likely result in a Barr body being observed in a cell nucleus?

Accepted Answer

A female with a normal XX karyotype

Question 19

Which of the following best explains why a fetus with no X chromosome does not survive in humans?

Accepted Answer

The X chromosome contains many essential genes unrelated to sex determination.

Question 20

A genetic counselor is analyzing a pedigree for red-green color blindness (X-linked recessive). If a color-blind woman and a man with normal color vision have children, what is the expected outcome for their sons?

Accepted Answer

All sons will be color blind.

Genetics Lecture 6: Sex Determination and Sex Chromosome Inheritance

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