Process by which organisms replicate themselves, assuring continuation of their species. The two basic forms are asexual and sexual. Asexual reproduction (e.g., fission, spore formation, regeneration, and vegetative reproduction) produces an offspring genetically identical to its single parent. Sexual reproduction produces a new individual through the union of special sex cells (gametes), usually from different parents. Gametes result from meiosis. Gamete union results in a zygote, the first cell of a new organism. Sexual reproduction ensures that each offspring is genetically unique (except in cases of multiple offspring derived from divisions of one zygote). Most animals, including all vertebrates, reproduce sexually.
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Premarital Conceptions, Postconception ("Shotgun") Marriages, and Premarital First Births: Education Gradients in U.S. Cohorts of White and Black Women Born 1925-1959
Jul 01, 2012; Abstract BACKGROUND In the U.S. today, premarital first births occur disproportionately to women with low education and income....