What is XYY syndrome or disease?

Extra Y chromosome. About one man in 1000 has an extra Y chromosome and it's likely to be discovered only if there's some investigation because of some problem such as autism. This has given rise to the myth that autism, criminal behavior and so forth are more common in such men. They average taller and tend to get worse acne. The "criminal" claims haven't held up to real science.

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I was wondering what is xyy syndrome or disease?

Aneuploidy. 47, xyy syndrome is a sex chromosome numeric abnormality or aneuploidy. Normally the cells of the body, barring sperm and egg, contain 22 pairs of somatic chromosomes and one pair of sex chromosomes (xx=girl, xy=boy) for a total of 46 chromosomes. Boys with an extra y are usually tall and may have learning disabilities and behavioral problems due to poor judgment/lower mean iq. Read more...
XYY. Junior gets two copies of dad's y-chromosome. Most xyy's are discovered incidentally. Reports of low iq may be ascertainment bias. Nobody questions these boys / men are tall and have nasty acne that needs to be treated. Despite "pop" claims of criminality, there are some national studies in which no xyy could be found who'd committed a crime with a weapon. Read more...

What exactly is xyy syndrome or disease?

Usually non-problem. This is a man with an extra y chromosome. These men tend to be tall and to have more troubles with acne than others. A junk-science paper and a false claim by murderer richard speck popularized the myth that these men tend to criminality. If there are no health problems, xyy almost never gets discovered except by prenatal screening; in the latter case it usually causes no troubles. Read more...