Question

If an individual has the genotype xxx, did non-disjunction occur in their mother or their father (or both) and at which division(s), meiosis i or meiosis ii? check all that apply:

Answer 1

The mother's genotype is XX and the father's XY. An individual that has the genotype XXX, if any non-disjunction happened, it occur in her mother because only from her mother, she could receive 2 Xs, while form her father, if a non-disjunction was to happen in this chromosomes, it would result in a XXY.
This non-disjunction happened during meiosis I, which is when the two copies of the same chromosome are taken each to a different cell. During this process, the separation did not happen on this two chromosomes being both Xs from the mother taken together to the new haploid cell. The non-disjunction on meiosis II only implies that the two chromatids from a chromosome did not separate and does not result in copies of the same chromosome.