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

> 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?

Pretty much this. Down’s syndrome is caused by having 3 copies of chromosomes 21. You could end up with 3 copies of any chromosome, but most cause an early miscarriage.

It’s a little more complex than the genes being “important” or not, but just having extra copies of those genes and making them more active isn’t fatal.