Despite 99% DNA similarity between humans and our nearest relative, chimpanzees, the locations of DNA swapping between chromosomes, known as recombination hotspots, are almost entirely different. The surprising finding is reported in a paper just published online in Science by Oxford University statisticians and US and Dutch geneticists.
This difference is intriguing because one of the central tenets of modern biology is that specific DNA sequences determine biological function. In most cases, when DNA sequence is highly similar between two species, the biological function of that DNA is predictably similar as well.
Recombination shapes the patterns of genetic variation in a species.It is the process by which genetic information inherited from a person’s two parents is mixed up to make one chromosome to pass on to their offspring. Chromosomes exist in pairs, with one chromosome of the pair inherited from the father, the other from the mother. At the point when sperm or eggs are made, the paired chromosomes line up and exchange pieces of DNA, recombining into a totally new, single chromosome, which is passed on to offspring.
In a previous study in Science, the Oxford team had identified many ‘hotspots’ along the human genome where this swapping of DNA is more likely to occur. Why these hotspots occur, and what triggers the swapping of DNA at those particular points, is a mystery. One theory was that the DNA code either side of hotspots controlled the activity. However, when the researchers compared chimps and humans for the new study, they were startled to find that despite being so genetically similar, the species have totally different recombination hotspots.
Professor Peter Donnelly at Oxford said: ‘If chimps and humans do not share these recombination hotspots, then it means something other than the surrounding DNA code must be controlling the process of recombination – because the surrounding DNA code in chimps and humans is pretty much identical. This means that recombination is even more mysterious than we already thought: what is controlling it, and why does it occur so often at these particular places?
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