sm pl biol
71modern synthesis — Biol. a consolidation of the results of various lines of investigation from the 1920s through the 1950s that supported and reconciled the Darwinian theory of evolution and the Mendelian laws of inheritance in terms of natural selection acting on… …
72multiple fission — Biol. fission into more than two new organisms. Cf. binary fission. [1910 15] * * * …
73Northern blot — Biol., Med. a procedure for studying the activity of a specific gene, as in testing for a hereditary defect: RNA fragments in an extract of a cell population or a tissue are separated by gel electrophoresis, transferred to a filter, and then… …
74nuclear membrane — Biol. the double membrane surrounding the nucleus within a cell. Also called nuclear envelope. [1885 90] * * * …
75parasexual reproduction — Biol. reproduction by recombination of genes from genetically dissimilar nuclei within binucleate or multinucleate cells, as in filamentous fungi. * * * …
76photic zone — Biol. the upper layer of a body of water delineated by the depth to which enough sunlight can penetrate to permit photosynthesis. [1970 75] * * * ▪ oceanography surface layer of the ocean that receives sunlight. The uppermost 80 m (260… …
77phylogenetic classification — Biol. classification of organisms based on their assumed evolutionary histories and relationships. Also called phyletic classification, phyletics. [1880 85] * * * …
78primary type — Biol. a specimen used in the original description or illustration of a species. * * * …
79primordial soup — Biol. 1. the seas and atmosphere as they existed on earth before the existence of life, consisting primarily of an oxygen free gaseous mixture containing chiefly water, hydrogen, methane, ammonia, and carbon dioxide. 2. a laboratory preparation… …
80radial symmetry — Biol. a basic body plan in which the organism can be divided into similar halves by passing a plane at any angle along a central axis, characteristic of sessile and bottom dwelling animals, as the sea anemone and starfish. Cf. bilateral symmetry …
