Would you like to pick your baby's gender?
One of my readers would, especially since she has two boys already. I am now asked to discuss Shettles' method of conceiving to increase your odds of having one of the sexes over the other.
The theory is that Y-sperm are fast swimmers, but are very fragile, particularly in an acidic setting. Thus if a couple is aiming for a boy (pun intended) they should have sex closest to the time of ovulation and use deep penetration, far away from the vaginal opening where the pH is relatively low. Conversely, those looking to have a girl should get going a few days before the egg is released (assuming the X-sperm endure while the Y- degrade) and deposit the goods along a more shallow domain.
The New England Journal of Medicine has discounted this theory after tracking the outcomes of over six hundred women who allowed their time of ovulation and sexual activity to be recorded and analyzed. You can read the summary here.
I know of people who swear by Shettles, though. "I had four girls in a row, we tried this method and now we have our boy" is one testimonial. Be that as it may, I think we over simplify things when we imagine sperm to carry ONLY the sex chromosomes as depicted above. I know people are guilty of this because time after time they attempt to support Shettles by saying things like, "You see, that X looks symmetric and sturdy whereas the Y has only one leg to stand on." Let's not forget that there are 22 other chromosomes packed in there which would, in my humble opinion, make the contribution of that tiny sex chromosome 'leg' negligible.
This is not to say that there isn't anything 'magical' about sperm. In fact, more and more research is being done on these gametes and the results have been fascinating to say the least. I once met a physician who was so renown in his field that he was given license to write about anything in a medical journal and chose to dedicate an entire article to sperm (totally unrelated to his field of study). The title was 'A Christmas Celebration for a Sexually Transmitted Fatal Condition,' that condition he's referring to is life itself. In this diatribe, he revels in the discovery of sacrificial and warrior sperm. The former type dies on the frontlines to neutralize the vaginal secretions (allowing their brothers to go forth) and the latter exist for the sole purpose of destroying sperm from other men!
Cue Pat Benatar's Love is a Battlefield.
2 comments:
This is fascinating stuff, thanks for sharing it. I don't get enough science in my life.
I'm going to show my ignorance here, but ... are X and Y chromosomes really shaped like an X and a Y?
Anne, the X really does look like an X. The Y looks more like a chef's hat than the letter.
There's an electron micrograph here for your viewing pleasure:
http://www.frontiers-in-genetics.org/pictures/chromosomes_xy_1.jpg
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