O.K. A student asked me a question the other day that stumped me and I bet there is a really simple answer.

We are talking about alternative inheritance patterns in humans, specifically sex-linked traits. I showed my class a karyotype in continuing to reinforce what chromosomes are and do. The karyotype was taken from a man that had XYY disorder.

The question was how does one go about inheriting the XYY disorder. I explained about nondisjunction during meiosis and subsequent formation of gametes. And also, I think the XYY disorder is actually not necessarily inherited genetically, it is just a mistake in meiosis. I believe that is true and the fact that XYY is supposedly inherited like some other human trait is a misconception. Then again, it is "inherited" to a certain degree in that it was due to a condition in the parent, of course by that logic so would FAS (Fetal Alcohol Syndrome.

SOMEONE PLEASE CORRECT ME HERE IF I AM WRONG.

Now for the real meat! How could a sperm be YY so as to fertilze an egg, resulting in XYY? The only result of a possible nondisjuction event in a male should be XY, right? In that case, XXY is an easy phenomenon to explain. But XYY cant really be explained, can it??????

I NEED SOMEONE TO HELP ME EXPLAIN HOW A "NONDISJUNCT" SPERM CELL COULD HOUSE A YY COMBINATION IN ORDER TO RESULT IN AN XYY PRODUCT.

Any help would be greatly appreciated. Thank you.