BIOL 2040 Lecture Notes - Lecture 11: Chromosome, Barr Body, Webbed Neck
1 Feb 2013
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X-inactivation: the embryos activate only one of the x-chromosomes and it is at random between maternal x and paternal x. It will still exist and it will still be replicated etc: epigenetics. Certain modifications at the levels of histones and dna keep the same x inactive (barr bodies) In cats, this will cause a mosaic for certain phenotypes. Only occurs in females because of the xx chromosome: 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: some inactive genes are not inactivated, genes expressed from the inactive x can contribute to distinguish phenotype. X and y can have crossing over and they are the homologous pairs that separate. 47 chromosomes, xxy: comes from extra x chromosomes, 1:1000 male newborns.
