Final answer:
The sex of offspring in birds and mammals is determined by a combination of both male and female genetics.
Step-by-step explanation:
In birds and mammals, the sex of the offspring is determined by the genetics of both the male and female.
In mammals, females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). In birds, females have two Z chromosomes (ZZ), while males have one Z and one W chromosome (ZW).
Therefore, the correct answer is c) A combination of both male and female genetics.