Question

If this trisomic fly is the progeny of a male fly of genotype (ey+ ey−, gw+ gw−) crossed to a female fly with genotype (ey− ey−, gw− gw−), what can you conclude about the events that led to its formation? if this trisomic fly is the progeny of a male fly of genotype ( , ) crossed to a female fly with genotype ( , ), what can you conclude about the events that led to its formation? nondisjunction occurred in the male parent at the meiosis ii division to produce an (n+1) sperm that fused with a normal (n) egg. nondisjunction occurred in the male parent at the meiosis i division to produce an (n+1) sperm that fused with a normal (n) egg. nondisjunction occurred in the female parent at the meiosis ii division to produce an (n+1) egg that fused with a normal (n) sperm. nondisjunction occurred in the female parent at the meiosis i division to produce an (n+1) egg that fused with a normal (n) sperm.

Answer 1

I found the exercise on the internet and attached is the representation of the fly's trisomy.

Correct answer:
"Nondisjunction occurred in the male parent at the meiosis I division to produce an (n+1) sperm that fused with a normal (n) egg."

It is during meiosis I that the homologous chromosomes are divided into two new cells. In this case, if a trisomy is present, it means that during this segregation part during meiosis I, two homologous chromosomes were not separated (nondisjunction) creating a gamete cell that had two copies of a chromosome (and another without any copy of that chromosome).
This error on meiosis I might have occurred in the male parent. As we can see from the schematic representation of the trisomy, there is two chromosomes with a wild allele (+). These alleles were only present in the male parent, as the female parent was homozygous for all genes, no wild allele (+).