a) In human male sperms produce 2 kids of sperms where in half the sperms carry X chromosomes and the other half carry the Y chromosome. Thus males are heterogametic. In human females, all eggs carry only X chromosmes. Thus they are called homogametic. When a sperm carrying X chromosome fertilizes the egg, the offspring would be a female and if a sperm bearing Y chromosome fertilizes the egg, the progeny turns out to be a male. In birds, males are homogametic ZZ while females are heterogametic.
b) Temperature does not influence *** in human beings. However, in some animals, it has a profound effect on ***. In crocodiles, low temperature induces femaleness and high temperature maleness. In turtles, temperature below 28ºC induced maleness, femaleness above 33ºC and equal number of males and females between 28ºC - 33ºC.