How does the presence of an extra chromosome 21 result in the characteristic craniofacial findings, developmental errors and other health issues?
I'd like to have an exact answer, because I can't seem to find a precise answer anywhere online, it seems all they mention is the fact that nondisjunction occurred during meiosis I. But I would like to know is why this extra chromosome creating so much complications?
It wouldn't make sense to talk about the position effect, so then I'd hypothesize that all the genes on chromosome 21 are over-expressed. How does this cause all the symptoms of Down's syndrome?
Thank you very much!