The sex of an animal is determined at fertilization. True or False?

The statement that the sex of an animal is determined at fertilization is true because the combination of sex chromosomes that occurs during this process establishes the genetic sex of the offspring. In many species, including mammals, birds, and some reptiles, the sperm (which can carry either an X or a Y chromosome) fertilizes an egg (which carries an X chromosome), resulting in the formation of a zygote with a specific combination of sex chromosomes. For example, if a sperm carrying a Y chromosome fertilizes an egg, the resulting zygote will typically develop into a male (XY), whereas if a sperm carrying an X chromosome fertilizes the egg, the offspring will be female (XX).

While there are species where the mechanisms of sex determination can differ, such as environmental or temperature-dependent sex determination in some reptiles, the general rule for most animals is that sex is determined at the point of fertilization based on the genetic material contributed by both the egg and sperm.