Question 1

Which of the following best explains why individuals with Klinefelter syndrome (XXY) have only one Barr body in their cells?

Accepted Answer

Because only one X chromosome is inactivated, following the N-1 rule where N is the number of X chromosomes.

Question 2

A female with Turner syndrome has a karyotype of 45,X. How many Barr bodies would you expect to find in her somatic cells?

Accepted Answer

Zero

Question 3

In mammals, what is the primary function of dosage compensation?

Accepted Answer

To balance the expression of X-linked genes between males and females

Question 4

According to the Lyon hypothesis, what is true about X-inactivation in female mammals?

Accepted Answer

It occurs randomly in each somatic cell early in embryonic development.

Question 5

Which gene is critical for initiating X-inactivation in mammals?

Accepted Answer

XIST

Question 6

In Drosophila, what determines the sex of an individual?

Accepted Answer

The ratio of X chromosomes to sets of autosomes

Question 7

A Drosophila fly has a karyotype of XXY:2A. What is its sexual phenotype?

Accepted Answer

Female

Question 8

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

Accepted Answer

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

Question 9

In Caenorhabditis elegans, what is the most common outcome of self-fertilization in hermaphrodites?

Accepted Answer

Nearly all offspring are hermaphrodites

Question 10

Which of the following best describes temperature-dependent sex determination (TSD) in reptiles?

Accepted Answer

The incubation temperature of eggs during embryonic development determines the sex of the offspring.

Question 11

A human cell with the karyotype 48, XXXY will have how many Barr bodies?

Accepted Answer

Two

Question 12

Which of the following is NOT a reason why X-inactivation does not fully prevent the symptoms of Turner or Klinefelter syndromes?

Accepted Answer

Not all X-linked genes are inactivated; about 15% escape inactivation.

Question 13

If a Drosophila has a chromosome composition of XO:2A, what is its sexual phenotype?

Accepted Answer

Male

Question 14

Which of the following best describes the N-1 rule for Barr body formation?

Accepted Answer

The number of Barr bodies equals the total number of X chromosomes minus one: $$N_{	ext{Barr bodies}} = N_X - 1$$

Question 15

A calico cat displays patches of orange and black fur. This is best explained by which genetic phenomenon?

Accepted Answer

Random X-inactivation in somatic cells

Question 16

Which gene acts as the master switch for sex determination in Drosophila?

Accepted Answer

Sxl

Question 17

In reptiles with temperature-dependent sex determination, which of the following is true?

Accepted Answer

Different temperature ranges during incubation can produce either males or females, depending on the species.

Question 18

Which of the following statements about Barr bodies is correct?

Accepted Answer

A Barr body is an inactivated X chromosome visible in the interphase nucleus of somatic cells.

Question 19

A geneticist observes a population of turtles in which all individuals incubated at temperatures below 28°C are male, and those above 32°C are female. What type of sex determination is this an example of?

Accepted Answer

Temperature-dependent sex determination (TSD)

Question 20

Which of the following is a consequence of a mutation in the Sxl gene in Drosophila males?

Accepted Answer

Lethality due to increased expression of X-linked genes

Sex Determination and Sex Chromosomes: Dosage Compensation, Chromosomal Ratios, and Environmental Effects

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