Gametes in humans are haploid. this means that they have half the number of chromosomes as normal body cells. sometimes, the gamete of a male and the gamete of a female combine to form a zygote that will eventually turn into a fetus. . phenotypic changes in a fetus may result . a. if a mutation occurs in the mother's brain cells. bubble . b. if a mutation occurs in the father's heart cells. bubble . c. only if a mutation occurs in both the mother's and father's cells. bubble . d. if a mutation occurs in the gametes.