I was trying to find out if men produced equal amounts of the x and y chromosone, and if factors like health, diet, or weather can affect the amount that either an x or y is produced.
Try looking here:
http://boards.straightdope.com/sdmb/showthread.php?threadid=30890
Neither health, diet, weather or dark of night can prevent these carriers from completing their appointed rounds.
The X’s to Y’s are a perfect 50/50.
When gametes(In men’s case, sperm) are made during Meiosis, they split in half, half of the chromosomes go into each cell, and usually no 2 homogolous pairs go together. (Homogolous means same type of chromosome, X and Y are a good example.)
(Rest is just cool info, read at own risk, you may get confused)
But there can be gametes with nothing or an X and a Y (Because of nondisjunction). The ratio of these are also 1:1.
So there are people who have XXX, XXY, X, and even XXXY(Very rare). There are no people with just Y’s because the X is in charge of growth of cells. (or at least the start)
FYI, that is also why men have nipples, because in the womb we all start as female because the X starts first.
Hold up there, Zygote! Are you suggesting that coconuts migrate?..Wait…wrong thread. Are you suggesting that men don’t have one less rib than women???
Weeeell, sorta. All babies do default to female. What really happens is that a gene on the Y c’some acts up and changes the direction of development. There’s nothing equivalent on the X to “start first”. It’s the Y gene that’s important.
Have you ever seen topless prepubescent boys and girls? Nipples look very very similar. It’s just that female nipples need that extra boost of estrogen et al at puberty to become, well, interesting.
I just heard that from a friend, didn’t really know the resoning.
Can’t blame me for trying, LoL.
Hm. What about this article then?
http://www.newscientist.com/ns/19991030/newsstory2.html
Without one copy of an X, the fetus won’t develop. Usually if there are any chromosomal abnormalities, the fetus won’t develop. Chromosome 21 is so small and unimportant that some people can survive having three copies of it, causing Downs syndrome.
Sex chromosomes abnormalities are also survivable.
Females have two copies of the X. That means that when the egg cell is developing and the chromosomes split, each egg gets one X.
Males have one X and one Y. That means that half the sperm have an X, and half have a Y. If an X sperm joins with an X egg, you have an XX female. If a Y sperm joins with an X egg, you have a XY male.
As you can see, one can survive with only one X chromosome, after all half the human species does. But it does cause problems…for instance, suppose you have a defective gene on your X chromosome…like a blood clotting protein. If you are a male, then you express the gene and are hemophiliac. If you are female, then you have a very good chance of having a back-up version on your other X, and will only be a carrier. If the hemophilia gene is in about 1% of the population, then one in a hundred of the men will be hemophiliacs, but .01 * .01, or one in ten thousand of the women will be hemophiliac.
But sometimes an egg or sperm has improper segregation of chromosomes, and you get double Xs or no Xs, or no Ys, or XYs.
If you get only one X (Turner syndrome), you will be phenotypically female without the masculinizing effects of the Y.
If you get XXX, known as a trisomy X leaves you female. Many XXX individuals are phenotypically normal or nearly normal, though the frequency of mental retardation is somewhat greater than normal.
XXY, or Klinefelter syndrome leaves you phenotypically male, but sometimes with some female secondary sexual charateristics.
XYY leaves you male. The study that found lots of prisoners with XYY didn’t mention that most XYYs are not criminals. Sometimes XYY are thought of as hypermasculine, but I don’t know how justified this is.
Y leaves you just plain dead, or rather you don’t get past the embryo stage. Without an X you don’t develop at all.
Of course, most of these syndromes leave you with health problems, sterility, increased risk for retardation, etc. But the rundown supports the claim that you “start” female, and the Y chromosome makes you male. Anyone without a Y develops as a female regardless of the number of Xs, anyone with a Y develops as a male regardless of the number of Xs. Also, some XYs (“males”) have a mutation that their bodies cannot recognize the hormone testosterone. These people are genetically male, but phenotypically female…they never develop male primary sexual characteristics. They have external genetialia like a female, but no uterus, and testes instead of ovaries.
And speaking of nipples, sometimes newborn babies of both sexes lactate, because their breasts have been affected by the mother’s lactatation hormones.
But there is a condition called meiotic drive where the proportion of Y sperm is increased. It’s basically a gene on the Y chromosome that preferentially causes all Y sperm to be made…meaning that if the mutation becomes established then only males are produced. It’s basically a takeover of chromosomal segregation by the Y. It is selected for because it gets twice as many copies of itself if it causes all Y’s. But if this happens, then all males who have the trait will have male offspring. They will all have male offspring. In a couple of generations (depending on the size) the whole population is male and the population goes extinct. Not good. This has been observed in rodents…the mutation gets established and soon you get only males.
Also, sex ratios are under genetic control, not just the random 50-50 of chromosomal segregation. So why don’t we see widely varying sex ratios? Answer: population genetics. Suppose you had lizards with 75% females/25% males. This would seem good, since you’d have lots more eggs…75% of the population could lay eggs instead of 50%. But what if you are a parent? If you lay a female egg, you have a normal fitness. But…if you have a male baby, then you will have three times as many grandchildren, since each male will on average mate with three females. If sex ratios are under genetic control, and your genes give you more male offspring, then your genes will take over, resulting in more males.
Now reverse it. If there are 25% females, 75% males, then on average only 1 out of 3 males will get to mate. You would have three times the fitness if you had female offspring. If the sex ratios are 50-50 then there is no selective advantage to having a male or female child, so it doesn’t matter what you have…there will be no selection either way. And, this is what we see in almost all animals, even species where 90% of the males never get to mate, like in elephant seals, or antelope. It would be advantageous to the species to get rid of all the extra males, but if there are fewer males it is advantageous for the individual to create more.
Does that answer your questions?
So there is nothing crazy like a diet rich in bananas that will make a male produce more X chromosone sperm? Or a warm climate that would cause a male to produce more Y? What got me wondering was something I once saw on TV about alligators that said the outside temperature would determine if the alligator eggs were male or female, and I was wondering if factors like that could sway the balance of X vs. Y.
What changes is probably not the number of each type of sperm, but the number that fertilize and egg. The two ways I can think of this happening is that the percentage of each that survive may be different, and the egg may accept one more readily than the other. I read somewhere that the proportion of male to female births varies very slightly with the age other the mother.
Male pilots of high performance jet aircraft (fighter planes and such) tend to have mostly female children. It’s not exactly known why, but possibly the high g forces are more detrimental to Y sperm than X sperm. Or maybe it’s the g-suits they wear or some other factor or combination of factors of flying these planes.
This may not help you much unless you want girls and can qualify to be a pilot.