Times Online: Genetic jot that makes us unique
Nature: Global variation in copy number in the human genome
Another interesting Nature paper out recently – I’m beginning to kick myself for not subscribing while I could have gotten the faculty rate! Fortunately this one’s free access for the moment. The take-home message is that in addition to the sequence of the human genome, we now have information about repetition within the genome – specific sequences, including genes, that display variable copy number across individuals, and perhaps ethnic groups.
Although this study could not directly link any of the variable regions to disease phenotypes (because the DNA donors involved were not assayed for diseases), some of the identified regions have previously been implicated in genetic disorders.
A few points about the study – first, it is not a shock that our DNA includes duplicated areas, nor that those areas could vary from individual to individual. But it is exciting that the number and extent of these variable copies is being systematically investigated. We haven’t had a good handle on what regions vary, nor what the implications of the extra copies are. They could affect the phenotype of the carrier in subtle or overt ways; the paper includes some educated guesses.
Second, I’ve heard some comments that this study “proves” we are not as similar to chimps as we thought. I disagree. The “99% DNA identity between humans and chimps” idea is based on incredibly strong conservation of the sequences of comparable genes between humans and chimps. It’s more like 96% identity when you take into account deletions and other differences, including the 50 or so human genes (out of around 25,000!) that are not intact in chimps. Just because we have additional variation in copy number – a type of variation found between human individuals, as well as between humans and chimps – does not weaken the evolutionary connection between humans and chimps.