This one, I hope will prove less controversial than the "What is a Jew?" thread I inadvertently started. Who knew?
Ed Pollak said: "As I suspected, something not mentioned in the NYT article is the fact that these copy number variations (CNVs) represent a genetic mosaic. They exist only in some tissues and not in others and represent copy errors during embryonic development." "Something analogous is responsible for true hermaphrodites in humans (i.e., individuals with both ovarian & testicular tissue)." Following Ed's lead, I discovered that the original article is available for free at http://www.ajhg.org/AJHG/abstract/S0002-9297(08)00102-X although it's not easy reading. The point about genetic mosaicism is interesting. If my understanding is correct, they found this CNV mosaicism in all 9 of 9 MZ twin pairs selected because they were discordant for Parkinsonism (which made success in their search much more likely). They also found it in at least one of 10 unselected concordant MZ twins (twin pair D). But in this study, they did not find it "in some tissues and not in others" as Ed suggested. Instead, they examined only nucleated blood cells, and it was within this tissue that they found "that these aberrations will typically occur in only a proportion of cells". In one twin, they found one type of aberration in 20% of the blood cells, and another type in 10-15% of blood cells. In the concordant pair D they found it in 70-80% of blood cells. There is also a less exotic example of mosaicism than true hermaphroditism. Only one of the pair of X-chromosomes found in every somatic cell of normal women functions, the other being randomly "X- inactivated". This means that a woman is actually a mosaic of two different cell lines each with a different working X-chromosome. Obligatory sexist joke: This explains why women are so complicated. Note added after Lyris rejection: There's another news report on the research at http://tinyurl.com/2f9jld or http://www.sciencentral.com/articles/view.php3?type=article&article_id=218 393078 Keep scrolling down to read, ignoring the annoying ads. It has not escaped my notice that the article quotes the author, Dumanski, as pointing out that the research has implications for the interpretation of twin studies. As I suggested in an earlier post, if MZ twins are not absolutely identical genetically, some part of the variation in characteristics between them must be genetic in origin. The standard interpretation is instead to claim differences between MZ twins indicates only environmental influence. Stephen ----------------------------------------------------------------- Stephen L. Black, Ph.D. Professor of Psychology, Emeritus Bishop's University e-mail: [EMAIL PROTECTED] 2600 College St. Sherbrooke QC J1M 1Z7 Canada Subscribe to discussion list (TIPS) for the teaching of psychology at http://flightline.highline.edu/sfrantz/tips/ ----------------------------------------------------------------------- --- To make changes to your subscription contact: Bill Southerly ([EMAIL PROTECTED])
