Question 1

Which of the following best explains why Klinefelter syndrome (47,XXY) individuals are phenotypically male?

Accepted Answer

The Y chromosome contains the SRY gene, which triggers male development.

Question 2

In Drosophila melanogaster, what is the expected sexual phenotype of an individual with the chromosome composition $$3X:2A$$?

Accepted Answer

Metafemale

Question 3

A calico cat displays patches of black and orange fur. Which genetic mechanism best explains this pattern?

Accepted Answer

Random X-chromosome inactivation (Lyon hypothesis)

Question 4

Which of the following is true regarding dosage compensation in mammals?

Accepted Answer

One X chromosome in each female cell is randomly inactivated, forming a Barr body.

Question 5

A young boy is diagnosed with hemophilia A, a recessive X-linked condition. Neither parent has hemophilia A. What are the most likely genotypes of his parents?

Accepted Answer

Mother is a carrier (X	extsuperscript{H}X	extsuperscript{h}), father is normal (X	extsuperscript{H}Y)

Question 6

Which region of the Y chromosome contains the gene responsible for initiating male development in humans?

Accepted Answer

SRY (Sex-determining region Y)

Question 7

In chickens, the heterogametic sex is the female (ZW). Which sex possesses the Y chromosome?

Accepted Answer

Neither males nor females

Question 8

A Drosophila fly has the following chromosome composition: $$X:2A. $$What is its sexual phenotype?

Accepted Answer

Male

Question 9

Which of the following best describes the mechanism of X-chromosome inactivation in mammals?

Accepted Answer

DNA and histone proteins are chemically modified to silence one X chromosome.

Question 10

In C. elegans, which of the following statements is correct regarding sex determination?

Accepted Answer

Hermaphrodites have two X chromosomes and no Y chromosome.

Question 11

Which of the following is a likely explanation for why individuals with Turner syndrome (45,X) are not phenotypically normal, despite X-inactivation?

Accepted Answer

Some genes on the X chromosome escape inactivation.

Question 12

Which of the following best describes the genetic balance theory in Drosophila sex determination?

Accepted Answer

Sex is determined by the ratio of X chromosomes to sets of autosomes.

Question 13

Which enzyme is directly affected by temperature in temperature-dependent sex determination (TSD) in reptiles, influencing the production of estrogens?

Accepted Answer

Aromatase

Question 14

A human cell with the karyotype 47,XXX will have how many Barr bodies?

Accepted Answer

$$2$$

Question 15

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

Accepted Answer

Gametes may have abnormal numbers of sex chromosomes, leading to syndromes such as Klinefelter or Turner.

Question 16

Which of the following statements about the Lyon hypothesis is correct?

Accepted Answer

Once an X chromosome is inactivated in a cell, all descendant cells have the same X inactivated.

Question 17

In humans, what is the chromosomal composition of a typical male?

Accepted Answer

46 chromosomes, including one X and one Y chromosome

Question 18

Which of the following best describes the outcome of self-fertilization in C. elegans hermaphrodites?

Accepted Answer

The majority of offspring are hermaphrodites, with a small percentage of males.

Question 19

Which of the following is NOT a mechanism of sex determination discussed in the study materials?

Accepted Answer

Mitochondrial inheritance

Question 20

A male horse is found to have two X chromosomes and no Y chromosome, yet is phenotypically male. What is the most likely explanation?

Accepted Answer

The SRY region must have translocated to the X chromosome.

Ch 5 Sex Determination and Sex Chromosomes: Mechanisms and Genetic Implications

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