Question 1

Which of the following best describes the mechanism of dosage compensation in humans?

Accepted Answer

One X chromosome is randomly inactivated in each somatic cell of females, forming a Barr body.

Question 2

A human with a karyotype of 47, XXY is most likely to exhibit which syndrome, and what are two common phenotypic features?

Accepted Answer

Klinefelter syndrome; tall stature and underdeveloped testes

Question 3

In Drosophila, what is the expected sexual phenotype of an individual with three X chromosomes and two sets of autosomes (3X:2A)?

Accepted Answer

Metafemale

Question 4

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

Accepted Answer

SRY (Sex-determining region Y)

Question 5

A calico cat displays patches of black and orange fur due to which genetic phenomenon?

Accepted Answer

Random X-chromosome inactivation in somatic cells

Question 6

In the Protenor mode of sex determination (XX/XO), what is the chromosomal composition of a male?

Accepted Answer

$$X O$$

Question 7

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

Accepted Answer

X-inactivation is random and occurs early in embryonic development.

Question 8

In humans, what is the expected number of Barr bodies in a cell from an individual with the karyotype 48, XXXY?

Accepted Answer

$$N - 1 = 3$$ Barr bodies

Question 9

Which of the following is true regarding sex determination in Caenorhabditis elegans?

Accepted Answer

Hermaphrodites are XX and males are XO.

Question 10

Which of the following best explains why individuals with Turner syndrome (45, X) exhibit phenotypic abnormalities despite X-inactivation?

Accepted Answer

Some genes on the X chromosome escape inactivation, and inactivation does not occur early enough in development.

Question 11

In birds, such as chickens, which sex is heterogametic and what is their sex chromosome composition?

Accepted Answer

Females; ZW

Question 12

Which of the following is a key assumption underlying the theoretical 1:1 sex ratio in humans?

Accepted Answer

Eggs are equally receptive to X- and Y-bearing sperm.

Question 13

A geneticist observes a population of reptiles in which incubation temperature determines the sex of the offspring. This is an example of:

Accepted Answer

Temperature-dependent sex determination (TSD)

Question 14

Which gene is considered the master switch for sex determination in Drosophila, and what is its primary function?

Accepted Answer

Sxl; induces female differentiation by controlling autosomal genes

Question 15

A human with the karyotype 47, XYY is most likely to exhibit which of the following characteristics?

Accepted Answer

Tall stature and possible personality disorders

Question 16

Which of the following best describes the function of the pseudoautosomal regions (PARs) on the Y chromosome?

Accepted Answer

They allow pairing and recombination with the X chromosome during meiosis.

Question 17

In the Lygaeus mode of sex determination (XX/XY), what is the chromosomal composition of a female gamete?

Accepted Answer

$$X$$

Question 18

Which of the following is true regarding dosage compensation in Drosophila melanogaster?

Accepted Answer

Male X-linked genes are transcribed at twice the rate of females.

Question 19

A researcher finds a Drosophila with a chromosome composition of $$2X:3A. $$According to the X:A ratio, what is the expected sexual phenotype?

Accepted Answer

Intersex

Question 20

Which gene is transcribed only on the inactive X chromosome and is critical for X-inactivation in mammals?

Accepted Answer

XIST

Sex Determination and Sex Chromosomes: Genetics Study Guide

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