Archive for September 14th, 2010

Picking out some sexy genes …

I know I’ve been writing a lot lately about the differences between men and women, and perhaps some readers are a bit fed up with the topic. Well, too bad, because today’s NYT reports new science shedding light on this often cloudy subject, and it’s looking more and more as if biology is the culprit.

Under Mendel’s laws of inheritance, you could thank mom and dad equally for all the outstanding qualities you inherited.

But there’s long been some fine print suggesting that a mother’s and father’s genes do not play exactly equal roles. Research published last month now suggests the asymmetry could be far more substantial than supposed. The asymmetry, based on a genetic mechanism called imprinting, could account for some of the differences between male and female brains and for differences in a mother’s and father’s contributions to social behavior.

Beginning way before the body produces a penis on a child destined to be male, the embryonic future dude may already be cherry-picking traits that have more to do with the end product that we have known.

In another novel pattern, she found sex differences in imprinted genes in different region of the brain, particularly those concerned with feeding and with mating behavior.

Sex differences in the brain are usually attributed to the influence of hormones, but sex-based differences in imprinting may be another mechanism by which nature spins male and female brains out of the same genome.

The research is, as it should be, heavy going with a lot of sciency stuff about imprinting … a sort of tuning out some genes while letting others do the driving.

A person gets one set of genes from each parent. Apart from the sex chromosomes, the two sets are equivalent, and in principle it should not matter if a gene comes from mother or father. The first sign that this is not always true came from experiments in which mouse embryos were engineered to carry two male genomes, or two female genomes. The double male and double female mice all died in the womb. Nature evidently requires one genome from each parent.

Biologists then made the embryos viable by mixing in some normal cells. The surprising outcome was that mice with two male genomes had large bodies and small brains. With the double female genome mice, it was the other way around. Evidently the maternal and paternal genomes have opposite effects on the size of the brain.

Hinting that there’s a difference between man and mouse, researchers are guessing that because of monogamy, fewer genes are imprinted … in humans … so less asymmetry?

Working in mice, the Harvard team showed that around 1,300 genes are imprinted. Dr. Dulac said that she expects a substantial, though lesser, proportion to be imprinted in people — maybe some 1 percent of the genome — because humans are more monogamous than mice and so the parents’ interests are more closely aligned.


Can it be true that millions of years of developing our big brains and thousands of years of socialization getting us all civilized and stuff have made such a difference?

Much of the available evidence comes from mice, and people may to some extent have emancipated themselves from imprinting when they evolved the pair bond system of mating about a million years ago. But the pair bond does not mean perfect monogamy, and in its deviations from perfection there is plenty of room for imprinting to thrive.

No shit.


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