>>25041205He's slightly wrong.
Gender in Gen II was based on a Pokémon's Attack DV. Shininess was Attack DV of 2,3,6,7,10,11,14,15 and all the rest at 10 (which incidentally comes out on 8/16^4, or 1/8192).
Gender was based on attack DV with the lower scores being females and the higher males (patriarchy). In 50/50 Pokémon, attack DV of 0-7 was female, 8-15 was male.
Pokémon with 12.5/87.5 gender ratios needed to be 0-1 attack DV to be female. Since you need at least 2 to be shiny, that meant 8:1 Pokémon could never be both shiny and female.
They rewrote the whole shit in Gen III, splitting DVs into IVs and PVs. IVs now did Hidden Power and stats, PVs did shininess and gender (and also new additions as natures and abilities).