Why does chromosome 21 seem relatively prone to abnormalities (ie-Down Syndrome)?

Question

So I’m aware there’s other possible abnormalities of other chromosomes such as ring shaped chromosome 20, but I’m wondering why down syndrome with chromosome 21 is so relatively common? What about it makes it more likely to get an extra/abnormality?

Edit: Seems to be equally common and it’s simply that because chromosome 21 doesn’t have very many “important” genes so babies with down syndrome can still survive, while the others will always miscarry or die shortly after birth. Confirm? thanks

In: Biology

Answer 1

Sounds like you have the right answer. Trisomy can happen in any chromosome, but most result in a non-viable fetus. This can also happen in the sex chromsomes (resulting XXX, XXY or XYY chromosomes) but these have less severe consequences than Down syndrome so they are not as apparent as Down.