Sex Determination and Sex Chromosomes

Question 1

Males are considered what when it comes to X-linked genes?

Answer 1

Hemizygous

Question 2

What is Swyer syndrome?

Answer 2

This is a condition when the SRY region of the Y chromosome is either mutated or deleted, this results in XY females.

Question 3

What does SRY code for?

Answer 3

Testis-determining factor

Question 4

Which ducts mature in XX individuals?

Answer 4

The Mullerian ducts

Question 5

Which ducts mature in XY individuals?

Answer 5

The Wolffian ducts.

Question 6

What are Y-linked traits termed? Give an example.

Answer 6

Holandric (wholly male) traits

Hypertrichosis pinnae

Question 7

What is the basic idea of dosage compensation in sex chromosomes?

Answer 7

Expression of genes on the X chromosome is equal between males and females due to X inactivation (randomly, lyon hypothesis) in females to form Barr bodies.

Question 8

What is the Xic region of the X chromosome? Describe the difference between the Xist and Tsix genes and their functions.

Answer 8

Xic region is the inactivation region that houses the Tsix and Xist genes.

Xist - code for Xist RNA, coats the X chromosome to inactivate

Tsix - antisense to Xist, makes Tsix RNA, inhibits Xist expression, no inactivation

Question 9

Is the # of Xic centers related to inactivation?

Answer 9

Yes, this doesnt occur in males with only 1 Xic region, but, when an extra Xic was inserted into the autosome of a male some of the cells had inactivated chromsomes.