If a pair of homologous chromosomes fails to separate during anaphase meiosis what is the chromosome number?

Question

Here is the full question. Thank You.

If a pair of homologous chromosomes fails to separate during anaphase meiosis what is the chromosome number of the four resulting gamets with respect to the normal haploid number (n)?

Answer 1

2

Answer 2

If the homologous chromosomes fail to separate, then the nondisjunction occurred in Anaphase I of meiosis (if the homologous chromatids failed to separate, then this would be Anaphase II).  So, from the nondisjunction in Anaphase I, one daughter cell will have two chromosomes (each with two chromatids) and the other daughter cell will not have that particular chromosome.  Thus, the resulting gametes will be of two types:  two which do not have the chromosome of interest and will be 0n in terms of that chromosome and the other two gametes will have two copies of the chromosome of interest and be 2n in terms of that chromosome.