If a parent has chromosomal abnormalities (such as a father with an XYY genotype) are their children at a higher risk of having chromosomal abnormalities as well?
They are. Since half his sperm will have two chromosomes in it, either an XY or a YY there is a 50% chance of inheriting and extra chromosome (XXY or XYY). This is because the mother will contribute an X. At anaphase I the XYY will divide into either XY and Y sperm, or YY sperm and X. At
fertilization, the mother gives an X, so the child can be:
XXY or XYY or XY or XX
So 50% chance of extra chromosome, and 50% chance of normal.
Since this answer was given, new information has been published about the fate of
the children of Kleinfelters fathers. Probability would say that there is a 50-50
chance of inheriting an abnormal gamete. But new research shows that this is not
the case in reality. The following link is to a paper written on this topic. It
turns out that only 1% of the gametes turn out to be abnormal. This raises new
questions, as often happens in science. For example, why? Where do the other
gametes go? Science is a process that is always subject to revision as new
information becomes available.
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Update: June 2012