fertilization

fertilization in biology, process in the reproduction of both plants and animals, involving the union of two unlike sex cells (gametes), the sperm and the ovum , followed by the joining of their nuclei. In the flowers of higher plants, the process occurs after pollination has enabled the sperm to contact the egg cell in the plant's ovary. In lower plants and in animals the sperm is actively motile and swims to the egg through an external aqueous medium or through a fluid environment within the reproductive tract of the female. The fundamental principle of fertilization is the same in all organisms. The first sperm to establish successful contact is absorbed by the ovum and the two nuclei unite, thus combining the hereditary material of both parents (see genetics ). In higher forms, the sperm contact initiates cell division in the fertilized egg (zygote), and the subsequent embryo develops into a new individual. Cross-fertilization indicates fusion of a sperm of one hermaphroditic plant or animal with an ovum of another, as distinguished from self-fertilization, in which ovum and sperm of the same individual are fused.

fertilization Key process in sexual reproduction during which the nuclei of female and male gametes (sex cells) fuse to form a zygote. The zygote contains the genetic material (chromosomes) from both parents (see heredity). In animals, the female sex cell is called the ovum and the male cell sperm. After fertilization, the zygote divides to form an embryo. Fertilization of the female ovum by the male sperm can be external (as in most fish, amphibians and aquatic invertebrates) or internal (as in reptiles, birds, mammals and insects). In plants, the male gamete is found in pollen, and for most higher plants, pollination occurs before fertilization.

fertilization The union of two gametes to produce a zygote, which occurs during sexual reproduction. Fertilization involves the fusion of two haploid nuclei (see HAPLOID NUMBER), containing genetic material from two distinct individuals (cross-fertilization) or from one individual (self-fertilization). The resulting zygote then develops into a new individual. Most aquatic animals, e.g. echinoderms, achieve fertilization externally, gametes uniting outside the body of the parents. Some other animals, particularly terrestrial species, have internal fertilization, with the union of gametes inside the female.