1. reproduction (2) 2. A discrete stage in succession of descent; e.g., father, son, and grandson are three g.'s. It may not be a unique designation, e.g., the offspring of an uncle-niece marriage is in the third generation in the paternal line but the fourth in the maternal line. [L. generatio, fr. genero, pp. -atus, to beget]
asexual g. reproduction by fission, gemmation, or in any other way without union of the male and female cell, or conjugation. See also parthenogenesis.heterogenesis (2), nonsexual g;
filial g. (F) the offspring of a genetically specified mating: first filial g. (symbol F1), the offspring of parents of contrasting genotypes; second filial g. (F2), the offspring of two F1 individuals; third filial g. (F3), fourth filial g. (F4), etc., the offspring in succeeding g.'s of continued inbreeding of F1 descendents.
nonsexual g. asexual g
parental g. (P1) the parents of a mating, commonly experimental, involving contrasting genotypes; the original mating of a genetic experiment; parents of the F1 g.
sexual g. reproduction by conjugation, or the union of male and female cells, as opposed to asexual g.
skipped g. a phenomenon of pedigrees in which a gene is transmitted from one affected person to another through a phenotypically unaffected person, as by recessivity (especially for X-linked traits), epistasis, variable expressivity, or absence of an environmental challenge such as a toxin. Except at a crass phenotypic level (e.g., clinical or commercial) this term becomes progressively less useful as the mechanisms are elucidated.
spontaneous g. the false concept according to which living matter can arise by the vitalization of nonliving matter. See also biogenesis.heterogenesis (3) ;
virgin g. parthenogenesis
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