Why would extra or missing chromosomes result to atypical phenotypes?

genetics
Answers:
trisomy 21 causes down syndrome, so it's an extra chromosome...

but... as to why that would result in anomalous phenotype.. i do not know.

as my science teacher would say whenever he doesnt know the answer to a question..
"it's still an live area of research"
Yes I think that having one smaller amount chromosome results in down syndrome.

I might be wrong because I haven't been taught it for a year and I'm partially asleep.. but that's what I remember from 7th grade.

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