Fundamentals of mammalian reproduction

Mammals reproduce sexually, and both sexes must unite to conceive offspring. The physical contact of both sexes does not constitute reproduction, but instead, it is the union of the sexual cells or gametes produced by each sex that constitutes the first step to reproduction. In females, the gamete is the egg or ovum. In males, the gamete is sperm. Each gamete contains one copy of each of the parental chromosomes, and thus, when the gametes unite, they form a zygote, the first complete cell of a new animal. Division of this first cell will result in the development of a full-grown animal. But before the two gametes can be united, several events must occur, all contributing to the phenomenon of mammalian reproduction. First, animals must find and choose mates. This very basic step will allow for a variety of adaptations to conquer, convince, attract, or seduce mates of the other sex. Second, mammals must get their gametes together, and this will be discussed under copulation and fertilization. Third, offspring growth and development to adulthood will be discussed under ontogeny and development. Because several aspects of development will be affected by the role of the two sexes, the importance and implications of mating systems will be discussed as well as strategies of reproduction and associated life history. Finally, some of the peculiar reproductive strategies present in mammals, and their role in the evolution and development of mammalian reproductive processes will be explored.

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