Human Heredity and Development_Walsh_Date_041310

Human Heredity and Development_Walsh_Date_041310 - X...

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X chromosome – gene dosage o Gene copies on X – females (2) XX; males (1) XY o BUT, do females have twice the amount of X-linked gene products? o Clotting factor is comparable. There must be some sort of dosage compensation to be operated. Females DON’T make twice as much X-linked. o How do we manage dosage compensation? Lyon Hypothesis o X-inactivation o Early in development o Random o Most of the genes on 1 of the 2 X-chromosome are inactivated o Inactivation passed to daughter cells in mitotic division o Not in germline cells that become gametes because it may have an inactive X How? o X inactivation center on X (Xic) o XIST gene XIST RNA binds to and inactivates X-chromosome (CH3 groups bind to DNA and prevent transcription) o Alters phenotype, not genotype (gene expression) o Why is XIST activated on only one X??? Still a mystery… X Chromosome and Barr Bodies o First seen in female cats in 1940 described by Murray Barr o You can see Barr Bodies in males as well
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Human Heredity and Development_Walsh_Date_041310 - X...

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