gene mutation question

forsdyke forsdyke at
Fri Jan 22 10:17:21 EST 1999

> Can someone define for me:  homozygous and hemizygous alterations?
> Thanks
> mseals at

For a diploid, you are homozygous if you have two equivalent copies of a
gene on homologous chromosomes. Operationally, this may mean that both
copies are expressed to produce identical products. Strictly, to be
homozygous the genes must have identical sequences, but this is not
necessary for producing identical products, because of the degeneracy of
the genetic code.

For a diploid to be hemizygous, it must be missing one copy of the gene,
or even a whole chromosome. The most obvious example of this is the X
chromosome in males.

Now for your definition. "Alterations". This presumably means a change
of some kind. A change from the existing state (homozygous or
hemizygous) to a new state. 

Hope this helps.

Donald Forsdyke, Discussion Leader. Bionet.immunology

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