Friday, October 3, 2008

The Sticky 21st Chromosome

"In the case of Down Syndrome the nondisjunction happens in chromosome 21 (Trisomy 21). Most of the time, the occurrence of Down syndrome is due to a random event that occurred during formation of the reproductive cells, the ovum or sperm. As far as we know, Down syndrome is not attributable to any behavioral activity of the parents or environmental factors. In 88% of cases, the extra copy of chromosome 21 is derived from the mother. In 8% of the cases, the father provided the extra copy of chromosome 21. In the remaining 2% of the cases, Down syndrome is due to mitotic errors, an error in cell division which occurs after fertilization when the sperm and ovum are joined."

I found this one fact to be quite interesting; that most of the time, it is the egg that has the extra 21st chromosome. Both women and men with Down Syndrome can be fertile, although both sexes have a reduced fertility rate. Where one parent has Down Syndrome, there is a 35% to 50% chance that the child would inherit the syndrome. This chance is even higher where both parents have Down Syndrome. There is also a high chance that pregnancy would end in miscarriage.

This is what Molly's Chromosomes look like:

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