Question 1

Which of the following best describes the mechanism of sex determination in humans?

Accepted Answer

Sex is determined by the presence or absence of the SRY gene on the Y chromosome.

Question 2

A woman who is heterozygous for the X-linked hemophilia allele (X$$^HX$^h) $$has children with a man who has normal blood clotting (X$$^HY). $$What is the probability that their son will have hemophilia?

Accepted Answer

$$0.25$$

Question 3

Which syndrome is characterized by the presence of a single X chromosome and no Y chromosome (XO), and what is a common phenotype?

Accepted Answer

Turner syndrome; normal intelligence and sterility

Question 4

In Drosophila melanogaster, what is the sexual phenotype of an individual with the following chromosome complement: XXY and two sets of autosomes (AA)?

Accepted Answer

Female

Question 5

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

Accepted Answer

Dosage compensation is achieved by inactivating one X chromosome in each female somatic cell.

Question 6

A calico cat is always female because:

Accepted Answer

The calico pattern results from X-inactivation in heterozygous females for X-linked coat color alleles.

Question 7

Which of the following best explains why an individual with the genotype XXY develops as a male in humans?

Accepted Answer

The SRY gene on the Y chromosome initiates male development.

Question 8

Which of the following is a direct consequence of nondisjunction during meiosis?

Accepted Answer

Formation of gametes with abnormal numbers of chromosomes

Question 9

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

Accepted Answer

Female; ZW

Question 10

A geneticist observes a human cell with three Barr bodies. What is the most likely sex chromosome complement of this individual?

Accepted Answer

XXXX

Question 11

Which region of the X and Y chromosomes is homologous and allows for pairing during male meiosis?

Accepted Answer

Pseudoautosomal region

Question 12

A woman with genotype X$$^wX$^+ ($$where X$$^w is $$the X chromosome with the white-eye allele and X$$^+ is $$the wild-type) is crossed with a man with genotype X$$^wY. $$What proportion of their daughters will have white eyes?

Accepted Answer

$$0.50$$

Question 13

Which of the following is true regarding the inheritance of X-linked recessive traits?

Accepted Answer

Affected mothers always pass the trait to all their sons.

Question 14

In Drosophila, what is the expected sexual phenotype of an individual with the chromosome complement XX and three sets of autosomes (AAA)?

Accepted Answer

Intersex

Question 15

Which of the following best describes a hemizygote?

Accepted Answer

An individual with only one copy of a gene or chromosome

Question 16

A male with Klinefelter syndrome has the following sex chromosome complement:

Accepted Answer

XXY

Question 17

Which of the following is a real-world example of environmental sex determination?

Accepted Answer

Sex in some reptiles is determined by temperature during embryogenesis.

Question 18

Which of the following is NOT a feature of X-linked inheritance?

Accepted Answer

Fathers pass X-linked traits to all their sons.

Question 19

Which of the following best explains why the chromosome theory of inheritance was supported by studies of nondisjunction?

Accepted Answer

Nondisjunction produces predictable patterns of inheritance that match chromosome behavior.

Question 20

A human cell with the sex chromosome complement XXXY would have how many Barr bodies?

Accepted Answer

3

Sex Determination and Sex-Linked Characteristics: Study Notes

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