I found the exercise on the internet and attached is the representation of the fly's trisomy.
Correct answer:
<span>"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 (n</span>ondisjunction)<span> 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 (+).</span>
Correct answer:
<span>"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 (n</span>ondisjunction)<span> 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 (+).</span>