I’m assuming that everyone knows the basics of sexual reproduction. Women produce eggs which have an X chromosome in them, because women have two X chromosomes. Men, who have an X chromosome and a Y chromosome, produce sperm with an equal percentage of X chromosomes and Y chromosomes. So, when the sperm fertilizes the egg, the sex of the baby depends on which sperm fertilized the egg. If it’s a sperm with an X chromosome, it’s a girl. If it’s a sperm with a Y chromosome, it’s a boy.
Now, some men have a syndrome called XYY syndrome, because they, instead of having an X chromosome and a Y chromosome, have an X chromosome and two Y chromosomes. It doesn’t really do much, but there’s some suggestions that men with XYY might have a higher incidence of learning disabilities and might be more aggressive.
Anyway, the average XY man produces an equal amount of X sperm and Y sperm, and has a 50/50% chance that any of his kids will be male or female. What about an XYY man? Is he more likely to have sons? Is it a 66/33% chance for him?
My brother is a “supermale.” He was diagnosed when he and his wife could not conceive. They never will in any conventional sense.
He had developmental problems as a boy and still has difficulty occasionally getting the words out of his brain and into his mouth. But he’s a very gentle person, so the agressive thing is probably a myth.
And the percentages thing is a non-starter too. It’s a fluke of one sperm, not all of them.
I don’t believe this is typical of XYY males. Generally, they’re quite normal, and usually don’t even know they have the syndrome. Percentage-wise, assuming all sperm are equally viable and competitive, there are four possible sperm genotypes, which should show up with equal frequencies: X, Y, XY, and YY. X and Y, of course, will give you a normal girl and boy. An XY would give you an XXY baby, which is Kleinfelter syndrome. And a YY sperm would produce an XYY baby, just like his dad.
Not all XXY guys are infertile, but enough are to cause there to be studies about them. Google directs you to some if you type in “xyy infertility.” This one says that the fertility of XYY men is dependant on “chromosome configuration in meiotic germ cells and the segregation pattern in sperm” which seems to indicate that there are differences in those amongst men with the extra Y.