Question 1

Which of the following statements best describes the chromosome theory of inheritance?

Accepted Answer

The transmission of chromosomes during meiosis accounts for Mendelian patterns of inheritance.

Question 2

In Morgan’s classic Drosophila cross, why were there no white-eyed females in the F2 generation?

Accepted Answer

The white-eye allele is X-linked and recessive, and females require two copies to express the trait.

Question 3

A human with the karyotype 47,XXY is most likely to exhibit which syndrome and what are typical characteristics?

Accepted Answer

Klinefelter syndrome; tall stature, rudimentary testes, and slight breast enlargement

Question 4

Which gene on the Y chromosome is responsible for triggering male development in mammals?

Accepted Answer

SRY gene

Question 5

What is the expected number of Barr bodies in a cell from a person with a 47,XXX karyotype?

Accepted Answer

$$2$$

Question 6

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

Accepted Answer

X0

Question 7

A woman whose father had hemophilia (an X-linked recessive disorder) marries a normal man. What is the probability that their first son will have hemophilia?

Accepted Answer

$$0.5$$

Question 8

Which of the following best explains dosage compensation in mammals?

Accepted Answer

Females inactivate one X chromosome in each cell, forming a Barr body.

Question 9

According to the Lyon hypothesis, what is true about X chromosome inactivation?

Accepted Answer

X inactivation is random in each cell, and all descendant cells maintain the same inactive X.

Question 10

Which of the following is a function of the pseudoautosomal regions (PARs) on the Y chromosome?

Accepted Answer

They allow synapsis and recombination with the X chromosome during meiosis.

Question 11

A karyotype analysis reveals a 45,X individual. Which syndrome is most likely, and what is a common clinical feature?

Accepted Answer

Turner syndrome; short stature and webbed neck

Question 12

In Drosophila, what determines maleness?

Accepted Answer

Ratio of X chromosomes to sets of autosomes (X/A)

Question 13

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

Accepted Answer

Mothers can be carriers and pass X-linked traits to both sons and daughters.

Question 14

A male with a 47,XYY karyotype is most likely to exhibit which of the following characteristics?

Accepted Answer

Over 6 feet tall and possible personality disorders

Question 15

Which process ensures that males and females have similar levels of X-linked gene products?

Accepted Answer

Barr body formation

Question 16

If a calico cat has patches of black and orange fur, what genetic mechanism explains this pattern?

Accepted Answer

Random X chromosome inactivation in females

Question 17

Which of the following best describes the genetic constitution of a female with Turner syndrome?

Accepted Answer

$$45,X$$

Question 18

During meiosis, what ensures that each gamete receives only one member of each homologous chromosome pair?

Accepted Answer

Segregation of homologs

Question 19

Which of the following is a direct result of the SRY gene being present in an embryo?

Accepted Answer

Development of testes from the gonadal ridge

Question 20

A woman with genotype $$X^H X^h ($$where $$X^H is $$normal and $$X^h is $$hemophilia) has a child with a normal man ($$X^H Y). $$What is the probability that their first daughter will be a carrier for hemophilia?

Accepted Answer

$$0.25$$

Sex Determination and Sex Chromosomes: Principles, Mechanisms, and Human Disorders

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