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Unformatted text preview: Mary Lyon hypothesised that the X inactivation happened at random early in development so that each female is composed of two populations of cells. In one population one X chromosome is expressed and in the other, the second X chromosome is expressed. Females are thus mosaics , i.e. composed of two genetically distinct cell populations. For genes which are homozygous this will make no difference but for genes for which the female is heterozygous the two populations of cells will be of opposite phenotypes. In this way she explained the patterns of hair colouration in, for instance, the tortoiseshell cat which is always female except for the very rare occurence of an XXY male, which exception proves the rule! (Those of you who are interested might like to try this well written page on cat coat colour genetics .)...
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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.
- Fall '10