Question

A human zygote (a fertilized human egg) has an abnormal sex chromosome genotype of XO meaning that the zygote only has a single X chromatid and no other sex chromosomes. This abnormal genotype could have resulted from (note: to earn full credit you must correctly select ALL that are possible for resulting in an XO zygote).

-a single nondisjunction event in meiosis I in the female parent

-a single nondisjunction event in meiosis II in the female parent

-a single nondisjunction event in meiosis I in the male parent

-a single nondisjunction event in meiosis II in the male parent

(Showing work on how to do this would be super helpful!)

Answer 1

the zygote has one X chromosome this is maybe from father or mother

1) if the X chromosome is from mother

then non-disjunction happened in father.non-disjunction can be in either meiosis I or meiosis II

homologous chromosomes separate during meiosis I, if X and Y chromosome failed to separate then one of the daughter cells, will have both X and Y chromosomes and the other daughter cell will have no X or Y chromosome, this daughter cell without sex chromosomes undergo meiosis Ii to produce 2 gametes without sex chromosome, if these gametes combine with gamete ith X chromosome from mother then XO zygotes can be formed

sister chromatids are separated during meiosis II,if the sister chromatidsof X chromosome failed to separate then one of the gametes formed from that cell will have 2 copies of the X chromosome and another gamete will have no X chromosome, if this gamete fuse with gamete with X chromosome from father then XO zygote can be formed.

2) if the X chromosome is from father

then non-disjunction happened in mother, non-disjunction can be in either meiosis I or meiosis II

homologous chromosomes separate during meiosis I, if 2 homologous X chromosomes failed to separate then one of the daughter cells, will have 2 homologous X chromosomes and the other daughter cell will have no X chromosome, this daughter cell without sex chromosomes undergo meiosis II to produce 2 gametes without sex chromosome, if these gametes combine with gamete ith X chromosome from father then XO zygotes can be formed.

sister chromatids are separated during meiosis II, if the sister chromatids of X chromosome failed to separate then one of the gametes formed from that cell will have 2 copies of the X chromosome and another gamete will have no X chromosome, if this gamete fuse with gamete with X chromosome from mother then XO zygote can be formed.

so the answers are

a single nondisjunction event in meiosis I in the female parent

-a single nondisjunction event in meiosis II in the female parent

-a single nondisjunction event in meiosis I in the male parent

-a single nondisjunction event in meiosis II in the male parent