ADP adenosine diphosphate. See adenosine phos- phate.
adrenal corticosteroid a family of steroid hor- mones formed in the adrenal cortex. There are more than 30 of these hormones, and all are synthesized from cholesterol by cortical cells that have been stim-ulated by the adrenocorticotropic hormone (q.v.).
adrenocorticotropic hormone a single-chain pep-tide hormone (39 amino acids long) stimulating se-cretion by the adrenal cortex. It is produced by the adenohypophysis of vertebrates. Abbreviated ACTH.
Also called corticotropin.
Adriamycin an antibiotic produced by Streptomy-ces peucetius that interacts with topoisomerase. DNA isolated from Adriamycin-poisoned cells contains single- and double-strand breaks. See gyrase, mitotic poison.
adult tissue stem cells See stem cells advanced in systematics, the later or derived stages or conditions within a lineage that exhibits an evolu-tionary advance; the opposite of primitive.
adventitious embryony the production by mitotic divisions of an embryonic sporophyte from the tis-sues of another sporophyte without a gametophytic generation intervening.
Aedes a genus of mosquitoes containing over 700 species, several of which transmit important human diseases. A. aegypti, the vector of yellow fever, has a diploid chromosome number 6, and about 60 muta-tions have been mapped among its three linkage groups. Among these are genes conferring resistance to insecticides such as DDT and pyrethrins (both of which see).
Aegilops a genus of grasses including several spe- cies of genetic interest, especially A. umbellulata, a wild Mediterranean species resistant to leaf rust. A gene for rust resistance has been transferred from A. umbellulata to Triticum vulgare (wheat).
aerobe an organism that requires molecular oxy-gen and lives in an environment in contact with air. aestivate to pass through a hot, dry season in a torpid condition. See also hibernate.
afferent leading toward the organ or cell involved. In immunology, the events or stages involved in acti- vating the immune system. Compare with efferent.
affinity in immunology, the innate binding power of an antibody combining site with a single antigen binding site. Compare with avidity.
affinity chromatography a technique for separat-ing molecules by their affinity to bind to ligands (e.g., antibodies) attached to an insoluble matrix (e.g., Sepharose). The bound molecules can subse-quently be eluted in a relatively pure state.
afibrinogenemia an inherited disorder of the hu-man blood-clotting system characterized by the in-ability to synthesize fibrinogen; inherited as an au-tosomal recessive.
aflatoxins a family of toxic compounds synthe-sized by Aspergillus flavus and other fungi belonging to the same genus. Aflatoxins bind to purines, mak-ing base pairing impossible, and they inhibit both DNA replication and RNA transcription. These my-cotoxins are highly toxic and carcinogenic, and they often are contaminants of grains and oilseed prod-ucts that are stored under damp conditions. The structure of aflatoxin G1 is shown.
Aflatoxin B1 has a CH2 substituted for the O at the position marked by the arrow. Aflatoxin B2 and G2 are identical to B1 and G1, except that the ring la-beled with an asterisk lacks a double bond.
African bees Apis mellifera scutellata, a race of bees, originally from South Africa, that was acciden-tally introduced into Brazil in 1957 and has spread as far as the southern United States. African bees are poor honey producers and tend to sting much more often than European bees. Because of daily differ-ences in flight times of African queens and European drones, hybridization is rare. See Apis mellifera.
African Eve See mitochondrial DNA lineages.
African green monkey See Cercopithecus aethiops.
agamete a haploid, asexual reproductive cell re-sulting from meiosis in an agamont. Agametes dis- perse and grow into gamonts (q.v.).
agammaglobulinemia the inability in humans to synthesize certain immunoglobulins. The most com- mon form is inherited as an X-linked recessive trait, which is symbolized XLA (X-linked agammaglobul- inemia) in the early literature. When O. C. Bruton described the condition in 1952, it was the first he- reditary immune disease to be reported. The disease.