CELS L17

Question 1

What does inactivated X condense into?

Answer 1

Barr body

Question 2

Where is the Barr body located?

Answer 2

Against the nuclear envelope in cells of females, but not in males.

Question 3

Are most genes on the inactivated X chromosome expressed?

Answer 3

No, most genes on the inactivated X chromosome are not expressed.

Question 4

What happens to the X chromosomes in Klinefelter’s male (n+1)?

Answer 4

All but one of the X chromosomes appear to be inactivated as Barr bodies.

Question 5

How many X chromosomes are inactivated in Klinefelter’s male (n+1)?

Answer 5

All but one X chromosome are inactivated

Question 6

In calico cats, what causes X-inactivation to be visible?

Answer 6

X-inactivation is visible because calico cats carry two different alleles (versions) of the fur color gene on the X chromosome and are heterozygous for that allele

Question 7

Are calico cats usually male or female?

Answer 7

Calico cats are almost always female, but rare male calicos exist due to genetic abnormalities, such as XXY (Klinefelter’s syndrome) affecting the sex chromosomes

Question 8

What fur colors do most male cats have?

Answer 8

Male cats typically have either black or orange fur, not both, unless they have a genetic condition affecting the sex chromosomes, like XXY

Question 9

What is a human example of X-inactivation effects in heterozygous human females?

Answer 9

Anhidrotic ectodermal dysplasia (absence of sweat glands) is a human example where the effects of X-inactivation can be seen in heterozygous females

Question 10

How do sex chromosomes differ in number between males and females in humans?

Answer 10

Females (XX) have twice as many X chromosomes as males (XY) and therefore have twice as many copies of X-linked genes.

Question 11

What is X-inactivation and why does it occur?

Answer 11

X-inactivation is a mechanism that compensates for differences in genetic dosage of X-linked genes in females. One X chromosome is inactivated in each cell early in embryonic development

Question 12

What is an inactivated X chromosome called, and what happens to its genes

Answer 12

An inactivated X chromosome is called a Barr body, and most of its genes are not expressed

Question 13

How does X-inactivation affect gene dosage in males and females

Answer 13

X-inactivation ensures that both males and females have the same effective dose (one active copy) of almost all X-linked genes