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Mosaicism

Gerard Tromp tromp at sanger.bcm.tju.edu
Sat May 20 18:58:19 EST 1995


To: wow24 at aol.com (Wow24)
Subject: Re: Mosaicism


	
	Mosaicism is not a disease per se, it is a state. It indicates that not 
all the cells of an organism that normally express a particular gene are 
expressing it. For disease-causing mutations, the founder (first person to have 
the disease or the parent of such an individual) may be mosaic. This means that 
the mutation occurred after the fertilized egg split into two or more cells. 
The mutation will, therefore, not be present in every cell. The body of the 
organism then has some cells with the mutation and some without, figuratively 
then like a mosaic, as in the pictures or decorations made of bits of tile or 
glass, just as the bits of glass or tile are not identical, so the cells of the
body do not have an identical genetic complement.

	The consequences of mosaicism can vary depending on the trait. An example
of harmless mosaicism was posted, i.e. the color variation of the calico cat
which is a consequence of inactivation of genes on the X chromosome. For genetic
disorders, the mosaic individual can often have a less severe disorder and may
even have no symptoms at all, depending on when during development the mutation
occurred. Some individuals mosaic for a mutation are only detected through
multiple affected offspring, and if the mosaicism for the mutation is restricted 
to their germline cells (the cells generating sperms and eggs), it may be 
difficult to demonstrate that they are mosaic for the mutation. For males, single
sperm PCR can be used.

	To reiterate, mosaicism in genetics indicates a condition where either 
all the cells of the body do not have the same genetic complement, or some the
expression of the same genetic complement is not the same for all cells of the
same tissue.

Gerard
-- 
Mailed and posted.

=======================================================================
Gerard Tromp, Ph.D.
Research Assistant Professor		Vox:	215-955-4487
Department of Biochemistry			215-955-4488 
	and Molecular Biology		Fax:	215-955-5393
Thomas Jefferson University
233 South Tenth Street, Room 328	E-mail:	tromp at sanger.bcm.tju.edu
Philadelphia, PA 19107 
U.S.A. 



-- 
=======================================================================
Gerard Tromp, Ph.D.
Research Assistant Professor		Vox:	215-955-4487
Department of Biochemistry			215-955-4488 
	and Molecular Biology		Fax:	215-955-5393
Thomas Jefferson University
233 South Tenth Street, Room 328	E-mail:	tromp at sanger.bcm.tju.edu
Philadelphia, PA 19107 
U.S.A. 



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