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A father with gene AC has a child with gene ACC. Where did the nondisjunction occur? (Meiosis I, Meiosis II, none of the above)

I do not know because both Meiosis I and II have the possibility of producing gametes with n+1. Is there something I'm missing here?

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  • $\begingroup$ It can happen during any of the two Anaphases. $\endgroup$
    – Tyto alba
    Feb 14 '17 at 4:38
  • $\begingroup$ There are three forms of nondisjunction: failure of a pair of homologous chromosomes to separate in meiosis I, failure of sister chromatids to separate during meiosis II, and failure of sister chromatids to separate during mitosis. Nondisjunction results in daughter cells with abnormal chromosome numbers (aneuploidy). $\endgroup$ Aug 29 '17 at 15:44
  • $\begingroup$ @zainabrija That's nice and all, but it doesn't really help me answer the question $\endgroup$
    – suomynonA
    Sep 4 '17 at 17:14
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Think about what gametes the father could have given the child. If the mother contributed an "A", then the father gave two "C"s, if the mother contributed a "C" then the father contributed an "A" and a "C".

In meiosis I, the father's chromosomes duplicate, so he has AA and CC - normally, at the end of meiosis I, these would be pulled into separate cells, so one of the resulting cells would be AA (and then in meiosis II, split into two further cells both with one "A") and CC (which in meiosis II splits into two further cells both with one "C"). The final result would be four gametes (sperm cells), two with "A"s and two with "C"s.

Since this is tagged "homework" I'm not going to give the final answer - but think about what phase of meiosis would have to go wrong to create an "AC" sperm, and what phase of meiosis would have to go wrong to create a "CC" sperm.

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  • $\begingroup$ AC - Meiosis 1 and CC - Meiosis 2? $\endgroup$
    – suomynonA
    Feb 15 '17 at 1:48
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    $\begingroup$ You got it! (Or I suppose to go with your username, I could also say "!ti tog uoY") $\endgroup$
    – Tapeworm
    Feb 15 '17 at 2:54

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