If two people with Downs Syndrome had a child, how many copies of chromosone 21 would he/she have?



Answers:
The 3 chromosomes would replicate once (they always only replicate once) and each egg/sperm could have either 1, 2, or 3 chromosomes depending on how the segregate during meiosis. 3 chromosomes can't segregate normally (1 to each like you get when there are only 2). So you can get different combinations. You can get 2,3,4,5, or 6 chromosomes. There's also the chance that all 3 remain together and so one sperm/egg gets no copy and the only copy(ies) would be from the other. So there are many combinations. Any baby that survives would either have 2 (the normal amount) or would have 3 and have downs syndrome as well. There are plenty of downs syndrome parents who have 'normal' children. Any more copies than 3 would cause severe abnormalities in the child and that pregnancy would never make it to term. Other trisomies besides Downs (3 copies of 1 chromosome only live a few months after birth). Having extra chromosomes and so extra dosages of the genes is very detrimental.

depends, mostly the child would have normal chromosomes-why are you trying (and failing) to be funny or are you genuinely interested?
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