CELS 191 Lecture 17

Question 1

which of the sex chromosome is smaller

Answer 1

y is smaller and has fewer genes

Question 2

what is the Lyon hypothesis (x-inactivation)

Answer 2

one X chromosome in a female (XX) is largely inactivated (not completely turned off).

Question 3

when does X-inactivation occur

Answer 3

early in development (roughly 100 cells)

Question 4

do daughter cells maintain the X-inactivation

Answer 4

yes - although of the 100 cells that are present when X inactivation occurs they all inactivated a different X chromosome so the female is a mosaic of maternal X and paternal X chromosomes

Question 5

inactivated X chromosomes condense into a _____. this is a highly condensed structure that lies against the ______ in cells of females, not males.

Answer 5

Barr body - nuclear envelope

Question 6

regardless of how many X chromosomes are possessed, all but one of them appear to be inactivated as Barr bodies. this shows us that ________________

Answer 6

the cellular mechanism can count how many X chromosomes there are and create the corresponding number of Barr bodies

Question 7

what is the only time male cats can be calico

Answer 7

if they have Klinefelter syndrome

Question 8

many genetic diseases map to the X chromosome . often diseases are more common in males because males have just one X chromosome whereas females have 2. most do not show a mosaic effect in heterozygous females because____

Answer 8

the gene product can be carried around the body. for example haemophilia A is a disease caused by the lack of blood clotting factors. if males have this gene they cannot produce the blood clotting factor however females are among the mosaic of cells with 2 different X chromosome so as long as one of those chromosome has the gene for the blood clotting factor it will be produced and carried around the body