A new study investigates the occurrence of genetic recombination in humans. The authors used a large set of individuals and discovered that there is a correlation between a mother's age and maternal recombination counts in her offspring. There are two possible explanations for this: either a woman's eggs have a higher recombination rate as she ages, or an egg with high recombination rate has a higher chance of being fertilized and finally born.
The authors reject the first hypothesis, as it makes some assumptions which have not been confirmed empirically, and conclude that eggs with higher recombination rates have a higher chance of being born. If this is true, then women whose eggs have higher recombination rates would produce more babies. After regressing family size on average recombination rate, this "selection hypothesis" is confirmed, even though the effect is modest, as many factors influence family size. Moreover, bylooking at sister pairs it is estimated that recombination rate has a heritability of ~30% in the group of women of this study. Therefore, it is likely that maternal recombination rate is a trait under positive selection.
Published online: 03 October 2004; doi:10.1038/ng1445
Recombination rate and reproductive success in humans
Augustine Kong et al.
Intergenerational mixing of DNA through meiotic recombinations of homologous chromosomes during gametogenesis is a major event that generates diversity in the eukaryotic genome. We examined genome-wide microsatellite data for 23,066 individuals, providing information on recombination events of 14,140 maternal and paternal meioses each, and found a positive correlation between maternal recombination counts of an offspring and maternal age. We postulated that the recombination rate of eggs does not increase with maternal age, but that the apparent increase is the consequence of selection. Specifically, a high recombination count increased the chance of a gamete becoming a live birth, and this effect became more pronounced with advancing maternal age. Further support for this hypothesis came from our observation that mothers with high oocyte recombination rate tend to have more children. Hence, not only do recombinations have a role in evolution by yielding diverse combinations of gene variants for natural selection, but they are also under selection themselves.