mosaicism - mosaicism If a mutation such as a chromosome...

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mosaicism If a mutation such as a chromosome loss occurs early in development, the descendents of the cell may represent a significant fraction of the individual who, being composed of cells of more than one genotype is a genetic mosaic . (And see also X inactivation in lecture 4.) Mosaicism is not infrequent in for instance the cases of Turner's syndrome or Down's syndrome described in the next lecture. Most mutations are recessive Why is this? Because most genes code for enzymes. If one gene is inactivated the reduction in the level of activity of the enzyme may not be as much as 50% because the level of transcription of the remaining gene can possibly be up regulated in response to any rise in the concentration of the substrate. Also, the protein itself may be subject to regulation (by phosphorylation for instance) so that its activity can be increased to compensate for any lack of numbers of molecules. In any case, if the enzyme does not control the rate limiting step in the biochemical pathway a reduction
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This note was uploaded on 11/22/2011 for the course CHEMISTRY CHM1025 taught by Professor Laurachoudry during the Fall '10 term at Broward College.

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