What is an example of an organism with genic sex determination?

Genic sex determination is a system in which the sex of an organism is determined by specific genes rather than by environmental factors or the presence of sex chromosomes, as seen in many other sex determination systems. Fungi provide a prime example of genic sex determination, as they often exhibit a mating type system that relies on specific genes rather than traditional male or female traits. In many fungal species, individuals can have multiple mating types, and the compatibility of these types, driven by genetic factors, determines the formation of fruiting bodies and sexual reproduction.

In contrast, birds have a system determined by ZW sex chromosomes, mammals have XY sex determination, and reptiles can often have an environmental component influencing their sex determination. Thus, fungi are highlighted as organisms that exhibit genic sex determination, making them the correct answer in this context.