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Scientists uncover 'totally crazy mechanism' behind much genetic diversity

UK scientists have shed new light on a gene that appears to drive much human evolution and genetic diversity. The research, published in the journal Nature Genetics, was led by the University of Leicester's Professor Sir Alec Jeffreys, the father of DNA (deoxyribonucleic acid)...

UK scientists have shed new light on a gene that appears to drive much human evolution and genetic diversity. The research, published in the journal Nature Genetics, was led by the University of Leicester's Professor Sir Alec Jeffreys, the father of DNA (deoxyribonucleic acid) fingerprinting. The gene is behind what Professor Jeffreys calls a 'totally crazy mechanism' that plays a key role in promoting genetic diversity. According to the researchers, the results should enhance our understanding of the processes that make us genetically unique, but which can also result in genetic diseases when they go wrong. At the heart of the study are so-called 'minisatellites', stretches of DNA that are characterised by much higher levels of genetic variation than other parts of the genome. These minisatellites, which Professor Jeffreys describes as 'pretty bizarre bits of DNA', are key to the success of DNA fingerprinting. Variations in the number of repeat units in minisatellites are unique to each individual (the obvious exception being identical twins). In this latest study, Professor Jeffreys and his team focus on the contribution of recombination to genetic diversity. When our bodies make egg or sperm cells, pairs of chromosomes (one inherited from our mother, and one from our father) line up and swap information. Sometimes this process goes wrong, resulting in genetic diseases. Minisatellites arise in hotspots of recombination activity. 'In each generation our genetic make-up gets 'reshuffled', like a genetic pack of cards, by a process called recombination - a fundamental engine driving diversity,' explained Professor Jeffreys. 'The work we have done over the past 10 years at Leicester has been key to understanding recombination in humans, and has allowed the molecular definition of recombination 'hotspots' - small regions in which the reshuffling process is focused.' The researchers focused their efforts on a gene called PRDM9 that is responsible for the production of a protein which binds to DNA and triggers hotspot activity. Different people have different versions of the PRDM9 gene, and the researchers were keen to find out if different versions of the gene would have different effects on recombination levels. 'The exciting finding is that people with different versions of PRDM9 show profoundly different recombination behaviours, not only in hotspots but also in chromosomal rearrangements that cause some genetic disorders,' said Professor Jeffreys. There is also a twist to this tale - the variation in PRDM9 is itself due to a minisatellite within the gene. As Professor Jeffreys points out, 'An intriguing possibility is that it is even driving its own evolution.' The study also appears to provide an answer to one of the mysteries surrounding recombination hotspots, namely their tendency to appear and disappear rapidly throughout evolution. 'We've shown that hotspots have a strange propensity for self-destruction, so how can they possibly exist? The PRDM9 minisatellite gives the answer - it evolves rapidly, like any other unstable minisatellite, and keeps churning out variants that can trigger new hotspots, replenishing those that have committed suicide,' commented Professor Jeffreys. 'A totally crazy mechanism to ensure that recombination keeps going, but typical of the weird solutions that evolution can throw up.'

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