Why are women the cause of down syndrome more often than men?

I know why down syndrome occurs, but why is it the case that women are usually the reason for contributing the aneuploid gametes?

{ 3 comments… read them below or add one }

tess July 31, 2010 at 3:15 am: beacause mens sperm are the same quality from puberty until they become infertile and womens eggs lose their quality as the age so the older the woman gets, the more chance she will have at conceiving a child with birth defects
Lisa A July 31, 2010 at 4:08 am: Sperm are produced continuously and are always fresh and young.
A person is born with all of the eggs that they will ever have already produced. That gives the eggs a lot of time to get damaged.
nutterorsaintuchoose July 31, 2010 at 5:06 am: well there is a problem with this as you can never ever find out which parent it came off so numbers would be just guessing as it happens at the moment of conception