Final answer:
Round worms do not use genotypic sex determination that involves chromosomes like birds or some reptiles. Instead of using the XY system as in mammals or the ZW system as in birds, round worms have different sex determination mechanisms.
Step-by-step explanation:
Genotypic sex determination does not occur in C) round worms. In mammals, sex is determined by the presence of XX chromosomes in females, which is homozygous, and XY in males, which is heterozygous. On the other hand, birds, some reptiles, and certain insects like butterflies and moths, utilize a ZW sex-determination system. In this system, ZZ (homozygous) results in a male and ZW (heterozygous) results in a female. The W chromosome is essential in determining sex, much like the Y chromosome in mammals.