mapped. Estimated genome size is 1.125 × 109 base pairs. See Appendix A, Chordata, Aves, Galliformes; Appendix E; comb shape, plumage pigmentation genes, poultry breeds. Galton apparatus an apparatus invented by Fran- cis Galton (illustrated below) consisting of a glass- faced case containing an upper reservoir where balls are stored. Below the reservoir are arranged row after row of equally spaced pegs that stand out from the wall, and below these is a series of vertical slots. The balls are allowed to fall one at a time through a central opening at the bottom of the reservoir. Since each ball after striking a peg has an equal probability of bouncing to the left or right, most will follow a zigzag course through the pegs and will eventually land in a central slot. The final distribution of balls in the slots will be a bell-shaped one. The apparatus demonstrates how the compounding of random events will generate a family of bell-shaped curves. See Appendix C, 1889, Galton.
gametangium an organ in which gametes are formed. See antheridium, oogonium. gamete a haploid germ cell. See Appendix C, 1883, van Beneden. game theory a mathematical theory dealing with the determination of optimum strategies where the policies adopted depend on the most likely behav- iors of two or more competitors. Game theory is employed in mathematical models of species com- petition. gametic disequilibrium the nonrandom distribu- tion into the gametes in a randomly mating popula- tion of the alleles of genes occupying different loci. The nonrandom distribution may result from linkage of the loci in question or because the loci interact with respect to their effects on fitness. See linkage disequilibrium. gametic meiosis See meiosis.
gametic mutation any mutation in a cell destined to become a gamete, and therefore potentially he- reditary. Compare with somatic mutation. gametic number the haploid number of chromo- somes (symbolized by N) characterizing a species. gametoclonal variation the appearance of new traits in haploid plants that grow in tissue culture from anthers or other reproductive material rather than from diploid body tissue as in somatoclonal variation (q.v.). gametocyte a cell that will form gametes through division; a spermatocyte or oocyte. gametogamy the fusion of gamete cells or nuclei. gametogenesis the formation of gametes.
gametophore a branch bearing a gametangium or gametangia. gametophyte the haploid phase (of the life cycle of plants undergoing an alternation of generations) during which gametes are produced by mitosis. See sporophyte. gamma chain one of the two polypeptides found in fetal hemoglobin (q.v.). gamma field a field where growing plants may be exposed to chronic irradiation from a centrally placed multicurie 60Co gamma-ray source. gamma globulin an antibody-containing protein fraction of the blood. See Appendix C, 1939, Tiselius and Kabat. gamma ray an electromagnetic radiation of short wavelength emitted from an atomic nucleus under- going radioactive decay. gamogony a series of cell or nuclear divisions that eventually lead to the formation of gametes. gamone a compound produced by a gamete to fa- cilitate fertilization. Chemotactic sperm attractants produced by eggs are examples.