x-linked genes

Question 1

Dosage compensation

Answer 1

organisms equalize gene expression of genes between members of different biological sexes

Question 2

Sex determination

Answer 2

the X and Y chromosomes pair during meiosis, even tho they are only homologous at pseudoautosomal regions

Question 3

XX-XY system

Answer 3

XX = female
XY = male
XO = female
XXY = male

Question 4

barr body

Answer 4

a condensed inactive X-chromosome
- XO females have no barr bodies, XXY males have 1 barr body, XXX females have 2 barr bodies

Question 5

Lyon hypothesis and X-inactivation

Answer 5

Mary Lyon proposed the random inactivation of one female X chromosome
- if cells contain more than 2 X chromosomes, all but one of them are inactive
-females are functionally hemizygous for X-linked genes at the cellular level

Question 6

hemizygous

Answer 6

diploid with 2 copies of genes but only one is active

Question 7

genes on X-chromosome example: calico cats

Answer 7

• orange gene is on the x chromosome
• O = orange, o = black
• due to barr bodies, either O or o allele may be blocked resulting in some cells being orange and some being black
• most calico cats are female since they have 2 copies of X so some cells will exhibit orange and some black

Question 8

x-inactivation

Answer 8

early in development, one x chromosome is randomly inactivated in each cell
- equally likely for paternal or maternal chromosome to be inactivated

Question 9

Mosaics in humans for X-linked genes example: red-green colourblindness

Answer 9

-females who have colourblindness confined to one eye have been reported
- female = x^cb/x male = x^cb/y
-females would be heterozygous and mosaics