>>19362001In humans and most animal species, there are only two types of gametes: the sperm (male) and the egg or ovum (female). There is no third type of gamete or a third corresponding developmental path for sexual reproduction.
The fundamental distinction in biological sex is based on the type of gamete an individual's reproductive organs are organized to produce:
— Sperm cells are small, motile (can move), and produced in large numbers. The developmental process is called spermatogenesis.
— Egg cells (ova) are large, non-motile, and produced in smaller numbers. The developmental process is called oogenesis.
The fusion of one sperm and one egg cell during fertilization forms a zygote, which then develops into a new individual.
While some simple organisms like certain fungi and algae exhibit isogamy (where gametes are of similar size and not classified as male or female, but as "+" or "-" mating types), complex organisms like humans use anisogamy (unequally sized gametes). In anisogamy, the existence of a third, intermediate gamete type is not observed in nature.
