Question

If Jack and Jill have a child with an Aaa genotype, during which meiotic division, and in which parent, could nondisjunction have occurred? Select all that apply Meiosis I in the mother Meiosis I in the mother Meiosis I in the father Meiosis I in the father Submit Request Answer

Answer 1

All the options are correct i.e. the correct answers are Meiosis I in the mother, Meiosis II in the mother, Meiosis I in the father, Meiosis II in the father.

Explanation: Nondisjunction in meiotic division produces abnormal gametes. Here the child has an Aaa genotype that means the child has three copies of one chromosome (2n+1). In the question, it is not mentioned that the alleles of the genotype Aaa are present on the sex chromosome. The abnormal gamete could be from either father or mother. Therefore the nondisjunction could have occurred in either the father or mother.

Now if the nondisjunction occurs during meiosis I, at least one pair of homologous chromosomes will not separate. Therefore among four gametes, two gametes will have an extra chromosome (n+1) and the other will have that chromosome missing (n-1). So, if the fertilization takes place between the gamete having one extra chromosome (n+1) and one normal gamete (n), the offspring will have three copies of one chromosome (2n+1).

Now if the nondisjunction occurs at meiosis II, at least one pair of sister chromatid will not separate. Therefore among four gametes, one gamete will have an extra chromosome (n+1), another gamete will have that chromosome missing (n-1), and the other two will be normal (n). So, if the fertilization takes place between the gamete having one extra chromosome (n+1) and one normal gamete (n), the offspring will have three copies of one chromosome (2n+1).

Therefore, all the options are correct.