Why does your chance of having a downs child increase as you grow old?

Old egg less perfect: Down syndrome begins with making eggs (or sperm), in which a "pre-egg" (or pre-sperm) cell with 46 chromosomes splits into 2 eggs (or 2 sperm). Each egg (or sperm) must get 23 chromosomes, but instead one egg gets both the #21 chromosomes and the other egg gets none. An egg with two #21's mated to a sperm with one #21 creates down syndrome: three #21's. Egg problem occurs more often in older moms.

Downs Syndrome: A woman's chances of giving birth to a child with Down syndrome increase with age because older eggs have a greater risk of improper chromosome division. By age 35, a woman's risk of conceiving a child with Down is 1 in 350. By age 40, it's about 1 in 100, by age 45, about 1 in 30. However, most children with Down syndrome are born to women under age 35 because younger women have far more babies.

Negatives accumulate: Girls are born with all the eggs they will ever have and these gradually mature and begin to release after puberty.The influence of environmental radiation, x-rays. drugs, and many unknown factors age and injure eggs. DS frequency increases with such accumulated influences.Why the same effect is not present for males is unknown.