Gender

From Pokémon Vortex Wiki

Pokémon gender was a concept introduced in Pokémon Vortex Version 3. Almost all species of Pokémon were assgined a gender, male or female. Gender makes no difference in the stats of a Pokémon, but the gender could affect evolution paths. One such example is Nidoran (M) and Nidoran (F).

Single-gender Pokémon

Gender-based evolutions

Certain Pokemon have to be a certain gender to evolve.