Question 1

Which syndrome is characterized by a karyotype of 47,XXY and typically results in tall stature, rudimentary testes, and partial feminization in humans?

Accepted Answer

Klinefelter syndrome

Question 2

In mammals, what genetic mechanism compensates for the difference in X chromosome gene dosage between males and females?

Accepted Answer

Random inactivation of one X chromosome in females

Question 3

A human cell with a karyotype of 48,XXXX would be expected to have how many Barr bodies?

Accepted Answer

$$N - 1 = 4 - 1 = 3$$

Question 4

Which gene on the Y chromosome is responsible for initiating male development in humans?

Accepted Answer

SRY

Question 5

In Drosophila melanogaster, what determines the sex of an individual?

Accepted Answer

Ratio of X chromosomes to sets of autosomes

Question 6

A female cat is heterozygous for X-linked coat color genes. According to the Lyon hypothesis, what pattern would you expect in her fur?

Accepted Answer

Mosaic patches expressing either maternal or paternal X alleles

Question 7

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

Accepted Answer

Sex is determined by incubation temperature during a critical period

Question 8

In humans, what is the most recent finding regarding the primary sex ratio (PSR) at conception?

Accepted Answer

Equal numbers of males and females are conceived

Question 9

Which region of the X chromosome is essential for X-inactivation and contains the XIST gene?

Accepted Answer

X inactivation center (Xic)

Question 10

A male child is found to have one Barr body in his cells and is color-blind. Which syndrome does he most likely have?

Accepted Answer

Klinefelter syndrome

Question 11

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

Accepted Answer

Metafemale

Question 12

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

Accepted Answer

X-inactivation occurs randomly in female somatic cells early in development

Question 13

Which gene is transcribed only in the developing testis of chickens and is essential for male development?

Accepted Answer

DMRT1

Question 14

What is the expected outcome if a human embryo has a karyotype of 45,Y?

Accepted Answer

Embryonic lethality

Question 15

Which of the following best explains why females with Turner syndrome (45,X) are not entirely normal despite X-inactivation in typical females?

Accepted Answer

Some genes on the X chromosome escape inactivation

Question 16

In mammals, what is the function of the testis-determining factor (TDF) encoded by the SRY gene?

Accepted Answer

Acts as a transcription factor to stimulate expression of other genes for male development

Question 17

Which of the following is a plausible explanation for the mosaic pattern of color blindness in heterozygous human females?

Accepted Answer

Random inactivation of one X chromosome in retinal cells

Question 18

In reptiles with temperature-dependent sex determination, which enzyme is most closely associated with the pathway leading to female development?

Accepted Answer

Aromatase

Question 19

Which of the following best describes the genic balance theory in Drosophila?

Accepted Answer

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

Question 20

Which of the following is true regarding the pseudoautosomal regions (PARs) of the human Y chromosome?

Accepted Answer

They share homology with regions on the X chromosome and are critical for segregation during meiosis

Sex Determination and Sex Chromosomes: Mechanisms and Variations

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