o The embryos activate only one of the x-chromosomes and it is at random between
maternal X and paternal X.
o It will still exist and it will still be replicated etc.
Certain modifications at the levels of histones and DNA keep the same X inactive
o In cats, this will cause a mosaic for certain phenotypes
Only occurs in females because of the XX chromosome
o Extra X is not as severe as extra autosomals
If all but one X chromosomes are inactivated, cells can have many X-
chromosomes without changing the phenotype of the cell
All extras are inactive Barr Bodies
o SOME INACTIVE GENES ARE NOT INACTIVATED
o Genes expressed from the inactive X can contribute to distinguish phenotype
Sex Chromosomes Pair at Meiosis
X and Y can have crossing over and they are the homologous pai