Azurill changes from a 25/75 ratio to a 50/50 ratio when evolving into Marill.
Burmy goes from a 50/50 ratio to either 100/0 or 0/100 upon evolution (Mothim and Wormadam respectively)
Kirlia goes from a 50/50 ratio to 100/0 upon evolution (Gallade)
Combee goes from a 87.5/12.5 ration to 0/100 upon evolution (Vespiquen)
Snorunt goes from a 50/50 ratio to 0/100 upon evolution (Froslass)
Salandit goes from a 87.5/12.5 ration to 0/100 upon evolution (Salazzle)
All except Azurill must be the gender that the ratio favours upon evolution. For instance, a male Combee can never become Vespiquen.
Source
Hope I helped!