a) longer exposure to chemicals in the environment - the dramatic rise after age 35 suggests other reasons
b) meiosis doesn’t work as well in older women - the cells that make the eggs would be older too
c) all of the above
d) none of the above
We weren’t taught the specific reasons for this in my medical genetics class, but I’m strongly leaning towards ‘b’. Down Syndrome is caused by a nondisjunction event during meiosis (Usually. There are certain classes of chromosome translocations that will result in Down Syndrome, even if there is no problem in the actual chromosome disjunction).
I’ll see if I can dig up some articles.
It’s not “the cells that make the eggs”, FYI - a woman is born with all of her eggs already.
According to this article, roughly 75% of maternal nondisjunction events leading to Down Syndrome occur in Meiosis I, and 25% in Meiosis II. A model has been proposed that this is due to age-dependent deterioration of some cellular factor necessary for proper spindle function.
Incorrect. A woman is born with all the oocytes she has (although, by the way, there is some current research showing that this is not entirely true), but oocytes are not eggs; oocytes are arrested in Prophase I. When triggered, they will continue through meiosis, eventually resulting in the release of three polar bodies and an ovum.