POKEMON GENDER VALUES

Every Pokemon is assigned a number (one byte, ranging from 0 to 255) that controls their gender. This is regardless of their gender ratio, so all-female Pokemon (like Chansey) and even genderless Pokemon (like Starmie) are given this number.

For Pokemon whose gender can be either male or female, there is a value known as the gender breakpoint which is the borderline between the determination of male and female. This breakpoint value varies depending on the gender ratio of that Pokemon. This table shows the possible ratios and breakpoints:

So in other words, if an Abra, whose gender ratio is 50% Male, 50% Female, has a gender value of 0 - 127, it will be female. If its gender value is 128 - 255, it will be male. The Psydex has a listing of the gender ratios for each Pokemon.

In Ruby, Sapphire and Emerald, Gender Values determine if Mirage Island can be seen.