Males of many animal species, including humans, are known to have shorter lifespans than females. Now, scientists from the University of California Berkeley (UCB),USA, believe they’re a step closer to understanding, thanks to male fruit flies.
UCB scientist Doris Bachtrog wanted to test the theory that the higher incidence of repeat genetic sequences on the Y chromosome (present only in male flies, whose sex chromosomes are XY) than on the X chromosome (female sex chromosomes are XX) was a causal factor in earlier mortality.
To learn this, Bachtrog studied male fruit flies (Drosophila miranda),which have a shorter lifespan and about twice as much repetitive DNA as female fruit flies.
Bachtrog demonstrated, in a study published in PLOS Genetics, that when DNA is tightly packed inside the cells of young fruit flies the repeat sequences are not active, but as the flies age their DNA becomes ‘looser’ and the repeat sequences are activated, producing ‘toxic side effects’ that advance ageing and ultimately death.
The study bolsters the notion that repeat sequences can be toxic, and that the Y chromosome is, in some sense, a ‘genetic liability’ that can hurry the process of ageing and degeneration.
More broadly, it supports evidence that repeat DNA may be a key player in the ageing process. For example, birds have far longer lifespans than they apparently ‘should’ – they have a 4 to 10-fold higher relativelifespan than mammals – and this is thought to stem from the relatively few repeat DNA sequences in avian genomes.
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