Question 1

Which of the following best describes the mechanism of sex determination in Drosophila melanogaster (fruit fly)?

Accepted Answer

The ratio of X chromosomes to sets of autosomes (X:A) determines sex.

Question 2

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

Accepted Answer

Inactivation of one X chromosome in females, forming a Barr body.

Question 3

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

Accepted Answer

$$2$$

Question 4

Which gene is responsible for initiating male development in humans, and where is it located?

Accepted Answer

SRY gene on the Y chromosome

Question 5

In the ZW sex determination system found in birds, which of the following is true?

Accepted Answer

Females are heterogametic (ZW) and males are homogametic (ZZ).

Question 6

A person with Klinefelter syndrome has the karyotype XXY. How many Barr bodies would you expect to find in each somatic cell?

Accepted Answer

$$1$$

Question 7

Which of the following best explains the mosaic coat coloration seen in female mammals such as calico cats?

Accepted Answer

Random inactivation of one X chromosome in each cell during early embryonic development.

Question 8

In honeybees, males are haploid and females are diploid. What is the genetic mechanism underlying this difference?

Accepted Answer

Males develop from unfertilized eggs, females from fertilized eggs.

Question 9

Which of the following karyotypes would result in a human individual with no Barr bodies in their somatic cells?

Accepted Answer

XO (Turner syndrome)

Question 10

A geneticist discovers a human with an XX karyotype who is phenotypically male. What is the most likely explanation?

Accepted Answer

A translocation of the SRY gene onto the X chromosome.

Question 11

In Drosophila, what would be the sexual phenotype of an individual with the genotype XX and three sets of autosomes (AAA)?

Accepted Answer

Intersex

Question 12

Which of the following statements about X chromosome inactivation is FALSE?

Accepted Answer

All genes on the inactivated X chromosome are expressed.

Question 13

Which syndrome is associated with the karyotype 45,X and what is the expected number of Barr bodies?

Accepted Answer

Turner syndrome; 0 Barr bodies

Question 14

Which of the following is a pseudoautosomal gene?

Accepted Answer

Mic2 gene

Question 15

In reptiles such as the American alligator, what environmental factor can determine the sex of the offspring?

Accepted Answer

Temperature during egg incubation

Question 16

Which of the following best describes the function of the Xist gene in X chromosome inactivation?

Accepted Answer

It encodes an RNA that coats the X chromosome and recruits proteins for compaction.

Question 17

A female with the genotype XXXX would have how many Barr bodies in each somatic cell?

Accepted Answer

$$3$$

Question 18

Which of the following is TRUE regarding the inheritance of pseudoautosomal genes?

Accepted Answer

They are inherited in a manner similar to autosomal genes.

Question 19

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

Accepted Answer

Presence of the SRY gene on the Y chromosome.

Question 20

In which of the following organisms does the paternal X chromosome get inactivated in females, rather than random inactivation?

Accepted Answer

Marsupial mammals

Sex Determination and Sex Chromosomes: Genetics Study Notes

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