On 18 March 2008 Chris Green wrote: > Have you been teaching your students that identical (monozygotic) > twins have identical genes? Turns out that's not correct. See this NYT article: > http://tinyurl.com/33m4c3
To which Tim responded: >[...] An important difference, yes. But a *big* difference? :) A bit of internet checking to see if another publication has a different angle on the subject brings up the following quote from the lead authors of the research, in "Science Daily": "The presumption has always been that identical twins are identical down to their DNA. That's mostly true, but our findings suggest that there are small, subtle differences due to CNV." http://www.sciencedaily.com/releases/2008/02/080215121214.htm So apparently the important finding (if confirmed, as always) is that there are significant differences in the DNA of identical twins, but these are small and subtle. This would seem to indicate that these DNA differences for monozygotic twins are not of the same order as those for dizygotic twins. In her comments on a related topic (schizophrenia and the Genain quadruplets) Joan Warmbold writes: > The fact that some of the sisters are more disturbed than others > suggests that environmental conditions also affect mental illness. Has anyone ever suggested otherwise? Apart from differential life experiences, I recall that one environmental difference that has been proposed as having an influence on the susceptibility to schizophrenia are hormonal effects during gestation. Unfortunately the academic articles I found on the internet on this subject require subscriptions. More generally, a research project that came up with the finding that in relation to vulnerability to schizophrenia "there was a highly significant gene-environment interaction" is reported by K-E. Wahlberg et al (1997): http://ajp.psychiatryonline.org/cgi/reprint/154/3/355.pdf Allen Esterson Former lecturer, Science Department Southwark College, London http://www.esterson.org >Subject: Identical twins? >From: [EMAIL PROTECTED] >Date: Tue, 18 Mar 2008 00:50:06 -0400 >Have you been teaching your students that identical (monozygotic) twins >have identical genes? Turns out that's not correct. See this NYT article: >http://tinyurl.com/33m4c3 >Chris Green >Subject: RE: Identical twins? >From: "Shearon, Tim" <[EMAIL PROTECTED]> >Date: Tue, 18 Mar 2008 01:50:58 -0600 >Chris- It is interesting indeed. But, truth be told, I don't really feel that >I understand it - certainly not from what is presented here. I haven't >read the research (oops. Another press conference before the article?) >- if I can! I think it would be unwise to ignore, yes. But if you take the > whole article, the quote that ends it is: >"This and other research, Dr. Witte said, shows 'you've got a *little bit* > more genetic variation than previously thought.' [emphasis mine] >In the meantime, a lot of biology textbooks may need updating. >Dr. Dumanski pointed out, for example, that as his study was going >to press, the following statement could be found on the Web site >of the National Human Genome Research Institute, the group that >financed the government project to decode the human genome: >'Most of any one person's DNA, some 99.9 percent, is exactly the > same as any other person's DNA. (Identical twins are the exception, > with 100 percent similarity).' >Doesn't this mean that we change that last sentence to 'Most of any >one person's DNA, some 99.9 percent, is exactly the same as any >other person's DNA. (Identical twins are the exception, with >99.9999 percent similarity).' >An important difference, yes. But a *big* difference? :) >Tim >Subject: RE: Identical twins? >From: Paul Brandon <[EMAIL PROTECTED]> >Date: Tue, 18 Mar 2008 10:06:51 -0500 >[...] >Depends on what's different. >Remember, our genetic overlap with chimps is 95-98%. >A few expresser genes can make a big difference. >PAUL K. BRANDON >Subject: Re: Identical twins? >From: "Joan Warmbold" <[EMAIL PROTECTED]> >Date: Tue, 18 Mar 2008 16:11:02 -0500 (CDT) >Keep in mind that schizophrenia is also influenced by the amount >of stress a child experiences in early childhood. I'm an identical >twin and our early experiences differed significantly as one became >the dominant one as well as more outgoing than the other--such >being my twin (Jean--get it, Jean and Joan). That all changed after >we moved and I was then able to establish my own identify without >constantly being compared to my twin--the pervasive annoyance >experience by for identical twins. I'm sure many of you have heard >of the Genain quadruplets who all became schizophrenic, no doubt >partly due to having an alcoholic father who terrorized, spied on >and sexually molested the girls. All four became schizophrenic before >age 25 (Rosenthal &Quinn, 1977). The fact that some of the sisters >are more disturbed that others suggests that environmental >conditions also affect mental illness. The sisters were followed for >over 60 years and, not surprisingly, the sister who was able to avoid >her father, Myra, was the least ill of the four (Mirsky, 2000). >Joan --- To make changes to your subscription contact: Bill Southerly ([EMAIL PROTECTED])
