The yellow-bodied trait has a chromosomal basis in sex and is only inherited in X-linked genes. I know this because a single copy of the mutant allele could produce the yellow body since males have only 1 X chromosome and no wild-type allele can mask it. But females could only have yellow bodies if both their X chromosomes carried the recessive allele, which would be impossible in the F2 generation because they would receive either one recessive allele from the father or the wild-type allele.