doug@hpcilzb.HP.COM (Doug Hendricks) (12/05/89)
Hello, I'm new to this net.group, but I have a heard something very strange and want a reference to any relevant articles. In the San Jose Mercury News (Dec. 3 Morning, 1989), on page 1P is an article by Charles A. Gardner, who "is conducting his doctoral research on the genetic control of brain development at the University of Michigan Medical School Department of Anatomy and Cell Biology." In this article, he states: "If a fertilized mouse egg from two white-furred parents goes through 4 cell divisions, the embryo will have reached the 16-cell stage. If this embryo is then brought together with a 16 -cell embryo from two black-furred parents, a ball of 32 cells is formed. This ball of cells will go on make a single individual with mixed black and white fur: one mouse with four parents..." ... "A similar event sometimes occurs naturally in humans when two sibling embryos combine into one. The resultant person may be completely normal." Mr. Gardner implies that such humans are known and identified. It is true? Do we have people walking around with two different genetic sets? Is there documentation? Mr. Gardner doesn't list any sources. His article was on another topic and he mentioned these genetic mosaic humans only to make a point. Actually, this idea is not entirely new to me. There is a form of Down's Syndrome called Mosaicism, where some portions of the person's body carry the normal 46 chromosomes and the rest of the person's body carries the 47 chromosomes of the common form of Down's Syndrome called Trisomy 21. Mosaicism (possibly misspelled), after "mosaic", is very rare, but documented. Sorry, I don't have references, my wife used to be a speech therapist who worked with people with Down's, and I just remember reading a pamphlet on the varieties of Down's Syndrome (Trisomy 21, 98% of cases; Translocation 15-21, most of rest; Mosaicism, very few).
dbell@cup.portal.com (David J Bell) (12/08/89)
Well, for a truly authoratative source, :{)
read Steve King's latest, "The Dark Half"...
The protagonist was one of those almost-twins, though the absorbtion
suposedly took place after quite significant differentiation of the
tissues was complete. Supposed to be unusual, but not that rare, for
MDs to pull pieces of what appear to be a sibling out of tumors, etc...
Dave dbell@cup.portal.commmm@cup.portal.com (Mark Robert Thorson) (12/09/89)
In the biology text I used in college, it was mentioned that there is a genetic condition which causes the absence of skin hair, and that in some women this can have a sort of patchwork appearance due to different expression of the X-chromosome. In women, one of the two X-chromosomes is not needed, and remains bundled up. (The unused chromosome is easily seen using staining and a microscope. Used as a test for gender, in those cases where it is uncertain.) Because the defective gene is on the X- chromosome, expression of skin hair reveals something like a genetic mosaic, in that it reveals which X-chromosome is being expressed where.
mike@uxf.cso.uiuc.edu (Mike Trogni) (12/10/89)
Mark Thorson is correct. All normal(1) women have two X chromosomes, one
donated from the mother & one from the father. Since twice of all the
genetic information would be too much, the somatic cells under X-inactivation,
randomly turning off one X chromosome, so if you study carefully traits
that are expressed by somatic cells that are determined genetically, you
will find that women are somatically anyway, a genetic amalgamation.
(1) Some genetic mishaps can occur and some women can end up with three
(or more) X chromosomes. Men can have XYY, etc. Some scientists used
to believe that men with XYY chromosomes had a tendency to be criminals!
--
[m-trogni@uiuc.edu]