Naked Science Forum
Life Sciences => Cells, Microbes & Viruses => Topic started by: pmailkeey on 23/06/2010 16:30:03
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pmailkeey asked the Naked Scientists:
Hi Chris,
"Is this all bollocks?"
It has been said that men (sperm) choose the sex of babies.
Are all sperm 'identical' or are there 'male-producing' and 'female-producing' sperm ? (If the latter, does one testicle produce one type and the other the other?)
If there are two varieties of sperm, these must be 'different'. Is it then not possible for the adult female to be able to 'attract' or guide one variety of sperm over the other - and hence influence the likelihood of a (fe)male offspring ?
Mike. (Naked as often as I can get away with it.)
What do you think?
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It is true that sperm are the determinant of the gender of the embryo that develops when an egg is fertilised.
This is because the genotype (chromosomal make-up) of a female includes two X chromosomes, whilst a male carries one X and one Y chromosome.
This means that when a female produces eggs by the process of meiosis, which adds one from each of the body's twenty-three pairs of chromosomes, females can contribute only X chromosomes to their eggs - so all (normal) eggs contain at least one X chromosome.
In males, however, because they carry an X and a Y, when sperm are produced, a random process - which is identical in both testicles, adds the X to some sperm and the Y to other sperm. This means that the sex of the future offspring is, quite literally, in the hands of the male, if that's the right phrase to use!
But what this means in practice is that the sperm that enter the female's body will comprise a mixture with roughly half carrying an X chromosome and half carrying a Y. When one of these fertilises the egg, the chromosomes carried by that sperm are added to those already in the egg, including the X or the Y.
The result is an egg with either two X chromosomes - which will produce a girl, or an X and a Y, which will cause the emrbyo to develop as a male.
Chris
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... guide one variety of sperm over the other - and hence influence the likelihood of a (fe)male offspring ?
http://en.wikipedia.org/wiki/Sperm_sorting
http://en.wikipedia.org/wiki/Ericsson_method
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Male producing sperm are stronger, faster swimmers but short lived. Female producing sperm are slower swimmers but longer lived. This means that if a man cools his testicles down before making love he will slow down all sperm. This means the male sperm will die before reaching the egg and the females will slowly swim to the egg and a girl baby will be produced. If the women puts her legs in the air or does a head or shoulder stand after sex this will help the faster swimming males reach the egg quicker. Aboy should result. I did this and got a boy. Not very scientific. Hubby wouldn't put the ice in his pants for the girl so we ended up with two boys.
Apparently sperm can be centrifuged and the two sexes separated. Can't remember which go to the top and which sink!!!
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I'm afraid that I am sceptical about the ice trick! The sperm that leaves the penis has come from within the male's body; much is stored in the seminal vesicles, so the temperature will almost certainly have normalised by the time the sperm leave the body; they'll also warm up pretty quickly inside the female, so I don't think this will work!
And as you have a 50% chance of a baby of either sex, the odds of two boys is actually quite high, regardless of ice or not!
Chris