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In the process, the nucleus of an egg is inserted into the cytoplasm of an egg from a donor female which has had its nucleus removed, but still contains the donor female's mtDNA. The composite egg is then fertilized with the male's sperm.
Sex Chromosomes X-Y. The male gametes or sperm cells in humans and other mammals are heterogametic and contain one of two types of sex chromosomes. Sperm cells carry either an X or Y sex chromosome. Female gametes or eggs, however, contain only the X sex chromosome and are homogametic.