Most people carry one or two genetic mutations that can cause early death or infertility in their offspring, researchers report in a study published on 8 April in Genetics1.
That estimate puts humans on a par with animals such as fruit flies2 and zebrafish3, which have smaller genomes. But it is probably a conservative figure, says lead author Ziyue Gao, a geneticist at the University of Chicago in Illinois.
Gao's team examined recessive mutations that cause lethal disease in people who inherit two copies of the flawed gene — one from each parent. People with one copy do not show symptoms, but can pass the mutation on to their children. The researchers' findings account for only mutations that would prevent a person from reproducing in the absence of modern medical care — excluding recessive conditions that do not always result in early death or infertility.