Q: Which formula correctly predicts the number of Barr bodies in a human cell?

$$N = \text{number of X chromosomes} - 1$$

Question 1

Which of the following best describes the fundamental difference between male and female gametes in sexually reproducing organisms?

Accepted Answer

Males produce small, motile gametes and females produce relatively large, immobile gametes.

Question 2

In the Protenor mode of sex determination, what is the chromosomal composition of a male?

Accepted Answer

$$12A + X$$

Question 3

Which of the following statements about the SRY gene is correct?

Accepted Answer

The SRY gene is found on the Y chromosome and triggers the formation of testes.

Question 4

A human with a 47,XXY karyotype will most likely exhibit which syndrome and phenotype?

Accepted Answer

Klinefelter syndrome; phenotypically male

Question 5

Which of the following best explains why calico cats are almost always female?

Accepted Answer

Calico coloration results from X-inactivation, and males have only one X chromosome.

Question 6

In Drosophila, what determines the sex of an individual?

Accepted Answer

The ratio of X chromosomes to sets of autosomes ($$X:A)$$

Question 7

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

Accepted Answer

One X chromosome in each cell becomes a Barr body, leading to dosage compensation.

Question 8

A person with androgen-insensitivity syndrome (AIS) has which of the following genetic and phenotypic characteristics?

Accepted Answer

XY karyotype; phenotypically female due to defective androgen receptor

Question 9

Which formula correctly predicts the number of Barr bodies in a human cell?

Accepted Answer

$$N = 	ext{number of X chromosomes} - 1$$

Question 10

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

Accepted Answer

Dosage compensation is achieved by doubling the transcription of X-linked genes in males.

Question 11

A researcher observes a population of turtles where incubation temperature determines the sex of the offspring. Which term best describes this mechanism?

Accepted Answer

Temperature-dependent sex determination (TSD)

Question 12

Which of the following statements about the pseudoautosomal regions (PARs) of sex chromosomes is correct?

Accepted Answer

PARs are regions of homology between the X and Y chromosomes that allow pairing during meiosis.

Question 13

A human embryo with a 45,X karyotype will most likely develop which syndrome, and what is a common feature?

Accepted Answer

Turner syndrome; short stature

Question 14

Which of the following best explains why the secondary sex ratio at birth is not exactly 1:1 in humans?

Accepted Answer

More males are conceived, but higher male mortality before birth leads to a lower male-to-female ratio at birth.

Question 15

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

Accepted Answer

Females; ZW

Question 16

Which gene is considered the master switch for sex determination in Drosophila melanogaster, and what happens if it is not properly expressed in females?

Accepted Answer

Sex-lethal (Sxl); lethality results if not properly expressed in females

Question 17

A geneticist is studying a case where a female mammal is heterozygous for an X-linked gene. What is the expected pattern of gene expression in her somatic cells?

Accepted Answer

Each cell expresses only one allele, leading to a mosaic pattern due to random X-inactivation.

Question 18

Which of the following is a key function of the X-inactive specific transcript (XIST) gene during X-inactivation?

Accepted Answer

It produces a long noncoding RNA that coats and inactivates one X chromosome.

Question 19

Which of the following best describes the effect of advanced paternal age (PAE) on the Y chromosome?

Accepted Answer

It is associated with an increased risk of mutations on the Y chromosome, contributing to disorders such as schizophrenia and certain cancers.

Sex Determination and Sex Chromosomes: Mechanisms and Genetic Implications

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