Final answer:
A population of a sexually reproducing species for population genetics purposes is defined as all individuals capable of interbreeding and producing viable, fertile offspring. Hybrids generally occur when members of closely related species reproduce. The presence of hybrids between similar species may indicate ongoing speciation.
Step-by-step explanation:
In the context of population genetics, a population of a sexually reproducing species can be correctly defined as all individuals capable of interbreeding and producing viable, fertile offspring. For the purposes of population genetics, species refers to a group of similar individuals that can interbreed with one another. Therefore, hybrids are typically produced when members of closely related species reproduce with one another. However, not all members of species can produce fertile offspring with individuals of other species; which is a critical point for defining a population within a species.
It is important to understand that individuals within a species share a more or less similar genetic makeup, but they are not genetically identical. The presence of hybrids between similar species suggests that they may have descended from a single interbreeding ancestral species, indicating that the speciation process may be ongoing.