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Lecture 11

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BIOL 2040
Motti Anafi

Lecture 11 Chromosome Aneuploidies  X-inactivation 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. o Epigenetics  Certain modifications at the levels of histones and DNA keep the same X inactive (Barr Bodies) 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
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