Sex Determination and Sex-linked traits Part 2

symbols for x-linked genes

similar to autosomal but denote which sex chromosome it is on

X^D

dominant mutation on X-chromosome

X^C

recessive

pseudominance

a recessive allele is not masked by the dominant so its traits are seen as a phenotype

gene dosage

• # of copies of a gene present in a genome

• amount of protein produced determined by ___

  • the optional amount for function

• If a # of gene changes → This changes → protein amount changes

unequal gene dosage

• nondisjunction results in cells with an unequal # of chromosomes

  • Somatic chromosome → usually lethal

  • gene expression of 1 chromosomes without gene expression of 2 chromosomes

X Inactivation

IX chromosome is activated (barr body)

what is barr body

inactivation X chromosome

who created Barr Body

Mary Lyon (Lyon Hypothesis)

X Inactivation & Female Mosaies

• RANDOM

• Once an 8 chromosome is inactivated, it is always inactive

Mechanism of X inactivation

• cell counts # of chromosomes

• one X is selected to be active; all others inactivated

what does Xist stand for

X-inactive specific transport

what is Xist-gene responsble for

• produces long RNA that represses gene expression

• main gene involved

X-Inactivation example

Calico and tortoiseshells cats