X-inactivation

Question 1

what is the X inactivation theory

Answer 1

one X chromosome in females is largely inactivated, the X chromosome is randomly selected early on in development and daughter cells maintain this inactivity through mitosis
- this happens because it balances the doses of X chromosome gene expression in both females and males
- X in activation has random patterns

Question 2

what is a Barr body

Answer 2

a highly condensed structure that lies against the nuclear envelope in cells of females but not in males

Question 3

what evidence proves the X inactivation theory

Answer 3

through the study of sex aneuploid conditions
- regardless of how many X chromosomes are possessed all but one of them appear to be inactivated into Barr Bodies

Question 4

how do calico cats display X inactivation

Answer 4

• X inactivation is visible in the cats as they carry 2 different alleles of the fur color gene (heterozygous for that gene)
• random inactivation of X chromosomes leads to the mosaic pattern
• once inactivation occurs all descendant cells will have the same X inactivation
• cailico cats are all female
• males are either orange or black