Question 1

Which of the following best describes the mechanism of sex determination in Drosophila melanogaster?

Accepted Answer

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

Question 2

A human individual with the karyotype 47,XXY will have how many Barr bodies in each somatic cell?

Accepted Answer

$$1$$

Question 3

Which of the following is a consequence of random X-chromosome inactivation in female mammals?

Accepted Answer

Females are genetic mosaics for X-linked genes.

Question 4

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

Accepted Answer

Females; ZW

Question 5

A female cat is heterozygous for an X-linked coat color gene. What is the most likely explanation for her patchy fur coloration?

Accepted Answer

Random X-chromosome inactivation during development.

Question 6

Which syndrome is characterized by a 45,X karyotype and what is the expected number of Barr bodies?

Accepted Answer

Turner syndrome; 0 Barr bodies

Question 7

In honeybees, what determines whether an individual develops as a male or a female?

Accepted Answer

Fertilization status of the egg (haploid/diploid)

Question 8

Which gene is critical for male sex determination in humans, and where is it located?

Accepted Answer

SRY gene on the Y chromosome

Question 9

A Drosophila fly has the following chromosome complement: $$XXY$$ and $$AA. $$What is its sexual phenotype?

Accepted Answer

Female

Question 10

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

Accepted Answer

They have a Y chromosome with the SRY gene.

Question 11

In mammals, what is the function of the Xist gene during X-chromosome inactivation?

Accepted Answer

It encodes an RNA that coats and inactivates the X chromosome.

Question 12

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

Accepted Answer

$$2$$

Question 13

Which of the following is true about pseudoautosomal regions of the X and Y chromosomes?

Accepted Answer

They allow pairing of X and Y chromosomes during meiosis.

Question 14

In certain reptiles, what environmental factor can determine the sex of the offspring?

Accepted Answer

Temperature during egg incubation

Question 15

Which of the following best describes dosage compensation in Drosophila melanogaster?

Accepted Answer

The level of expression of genes on the X chromosome in males is increased twofold.

Question 16

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

Accepted Answer

Translocation of the SRY gene to the X chromosome.

Question 17

Which of the following is a property of Barr bodies?

Accepted Answer

They are inactivated X chromosomes visible in the nucleus.

Question 18

In the X-0 sex determination system found in some insects, what is the chromosomal composition of a male?

Accepted Answer

XO

Question 19

Which of the following best explains why only one X chromosome remains active in human somatic cells, regardless of the total number of X chromosomes?

Accepted Answer

A counting mechanism ensures only one X chromosome remains active.

Question 20

A Drosophila fly has the following chromosome complement: $$XO$$ and $$AAA. $$What is its sexual phenotype according to the X:A ratio?

Accepted Answer

Metamale

Sex Determination and Sex Chromosomes

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