Trisomy is having three copies of a chromosome. It is caused by a failure of disjunction during meiosis, with unequal separation of chromosomes between the gametes. Nearly all types of trisomy are rapidly fatal, causing early abortion. Of the three trisomies which survive to birth, only trisomy 21 - Down's syndrome - tend to survive to older than one year.
Incidence of all trisomies increases with maternal age, suggesting some relationship with the amount of time the oocyte spends in suspended meiosis.
Annotations allow you to add information to this page that would be handy to have on hand during a consultation. E.g. a website or number. This information will always show when you visit this page.