the  determination of an offspring is of 3 types
1.environmental:incubation of eggs 
eg:lizards
2.chromosomal:as in humans
3.genic:presence of fertility gene results in male.
i didn't understand genic method.also give me an eg

In many species, sex determination is genetic, that is, males and females have different genes that determine their sex. Since the genes are different, it follows that the chromosomes are also different. Various combinations are observed such as XY (in man), ZW (in some birds, reptiles and insects), and XO (in grasshoppers and crickets). The different genes trigger sexual dimorphism.