Identical twins have up to 12% difference in their DNA
I suspect this is balls. Of course it depends how you measure differences (if I have three copies of chromosome X, which is ~150 million base pairs long, does that mean that my DNA is 5% different to yours), but 12% is still a massive figure.
Here's the paper, which is looking at differences between monozygotic twins in two families in terms of changes in copy number and single nucleotides.
The copy number variants are summarised in tables 1 and 2 - the differences between twins have a yes in the mitosis column (as they arose during developmental cell divisions). I can't be bothered to add up the figures exactly, but there's ~20 differences and they're all under a megabase, so it's certainly no more than 15Mb or so. The human genome is about 3000Mb, so that's about 0.5% at most.
The SNP differences are covered here: "The genotypes generated by the Affymetrix 6.0 array have also allowed us to establish that ~0.12% (1086 and 1022 in twin pair 1 and 2 respectively; 11 substitutions shared by both pairs) of the SNPs in the twins represented de novo substitutions." I can't work out what their definition of a de novo substitution is, but let's assume it's the same as for copy number, which means that 0.12% of the variation in the twin pairs is not present in the parents, and they say ~65% of that is down to parental meiosis so it will be present in both of the twins, so we're down to about 0.8% difference, or about 700 base positions. Out of 3 billion.
The 12% figure is either a typo for 0.12%, although even that isn't correct, or they've fished the figure out of the introduction ("CNVs may account for a major fraction (~12%) of the genome"). That sentence isn't even talking about their results but just general population variation. It references two further papers, and while I haven't gone through them thoroughly I don't think either of the two cited papers actually support that figure, and they're also papers from 2004 when the technology has moved on massively since then.
Sorry, that was longer than I intended, but I hate shoddy reporting of papers, especially when it's probably based on a dodgy press release.
Yeah, the 12% figure threw me too given that the common figure bandied about in the media that we share over 90% of our DNA with chimpanzees. I suspect that identical twins will share more DNA with each other than with a different species.
-- Steve wishes he could trust media reporting more... because it's starting to feel less like cautious skepticism and more like paranoia these days.
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I suspect this is balls. Of course it depends how you measure differences (if I have three copies of chromosome X, which is ~150 million base pairs long, does that mean that my DNA is 5% different to yours), but 12% is still a massive figure.
Here's the paper, which is looking at differences between monozygotic twins in two families in terms of changes in copy number and single nucleotides.
The copy number variants are summarised in tables 1 and 2 - the differences between twins have a yes in the mitosis column (as they arose during developmental cell divisions). I can't be bothered to add up the figures exactly, but there's ~20 differences and they're all under a megabase, so it's certainly no more than 15Mb or so. The human genome is about 3000Mb, so that's about 0.5% at most.
The SNP differences are covered here: "The genotypes generated by the Affymetrix 6.0 array have also allowed us to establish that ~0.12% (1086 and 1022 in twin pair 1 and 2 respectively; 11 substitutions shared by both pairs) of the SNPs in the twins represented de novo substitutions." I can't work out what their definition of a de novo substitution is, but let's assume it's the same as for copy number, which means that 0.12% of the variation in the twin pairs is not present in the parents, and they say ~65% of that is down to parental meiosis so it will be present in both of the twins, so we're down to about 0.8% difference, or about 700 base positions. Out of 3 billion.
The 12% figure is either a typo for 0.12%, although even that isn't correct, or they've fished the figure out of the introduction ("CNVs may account for a major fraction (~12%) of the genome"). That sentence isn't even talking about their results but just general population variation. It references two further papers, and while I haven't gone through them thoroughly I don't think either of the two cited papers actually support that figure, and they're also papers from 2004 when the technology has moved on massively since then.
Sorry, that was longer than I intended, but I hate shoddy reporting of papers, especially when it's probably based on a dodgy press release.
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-- Steve wishes he could trust media reporting more... because it's starting to feel less like cautious skepticism and more like paranoia these days.