If it is a human zygote with no mutations, then it will contain 46 chromosomes. Each parent gives the zygote 23 chromosomes. All human gametes without mutations contain 23 and when joined during fertilization they form a zygote with 46 chromosomes. However, chromosome number varies by species, for example a normal pigeon zygote would have 80 chromosomes. All zygotes have their adult number of chromosomes, once again assuming there are not mutations. See the related links for a list of the adult and thus the zygote number of chromosomes.