Sex determination

Genotype	Human	Drosophila
XX	female	female
XY	male	male
XXY	male	female
XO	female	male

Heterogametic males
     Mammals (including humans)
          Male gender determined by presence of Y chromosome
     Drosophilid flies
          Gender determined by ratio of X chromosome to autosomes
Heterogametic females--birds
Environmental sex determination
     Reptiles
          Temperature of nest often determines sex ratio of hatchlings

mating box turtles