Sex selecting your litter
D. Caroline Coile, Ph.D.
Aristotle preferred the natural approach: Have sex in either the north or the south wind, depending on the desired results. Hippocrates went for the scientific approach: Tie a string around either the right testicle or left testicle (don't try this at home).
More recent methods have been far less exotic but have built on our knowledge of DNA. Once the discovery of the X and Y chromosomes was made, the problem became how to favor one type of chromosome over the other in the race to the egg.
One fo the all-time most popular do-it-yourself tecniques for people, the so-called Shettles method, championed by Landrum Brewer Shettles, was based upon the observation that a Y-bearing sperm is lighter than an X-bearing sperm and therefore faster swimming but less hardy. The idea was that anything that lowered sperm count, such as frequent ejaculation, would lower the Y count first. Anything that requred sperm to hang around a long time before meeting the egg, such as intercourse several days before ovulation, also would lower the sperm count. These methods--often suggested together--would supposedly increase the chances of producing a girl. The opposite would be true for favoring Y sperm, so couples who wanted a boy were advised to abstain from sex until immediately before ovulation, when they shuold have intercourse. Shettles claimed 75 percent success with his methods, but subsequent studies failed to support its success.
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