Alcohol dehydrogenase (ADH)
is integrated into the plant genome, and here it in- duces changes in metabolism and tumor formation. The genome of strain 58 of A. tumefaciens was se- quenced in 2001 by a group led by E. W. Nestor. Its genome contained 5.67 mbp of DNA distributed among four replicons: a circular chromosome (CC), a linear chromosome (LC), and two plasmids (pAt and pTi). The plasmids are DNA circles, and most of the genes responsible for crown galls are on pTi. The Table lists the general features of the four repli- cons.
Strains of A. tumefaciens carrying the plasmid may be artificially genetically engineered to introduce foreign genes of choice into plant cells, and then by growing the cells in tissue culture, whole plants can be regenerated, every cell of which contains the for- eign gene. See Appendix A, Bacteria, Proteobacteria; Appendix C, 1907, Smith and Townsend; 1981, Kemp and Hall; 2001, Wood et al.; Appendix E; Ti plasmid.
Agropyron elongatum a weed related to crabgrass noted for its resistance to stem rust. Genes confer-ring rust resistance have been transferred from this species to Triticum aestivum (wheat).
AHC Achilles’ heel cleavage (q.v.).
AHF antihemophilic factor. See blood clotting.
AI, AID, AIH See artificial insemination.
AIA anti-immunoglobulin antibodies, produced in response to foreign antibodies introduced into an ex- perimental animal.
AIDS the acquired immunodeficiency syndrome, a disease caused by the human immunodeficiency vi- rus (HIV). This virus attacks lymphocytes of helper T subclass and macrophages. The depletion of these cells makes the patient susceptible to pathogens thatwould easily be controlled by a healthy immune sys- tem. The infection is transmitted by sexual inter- course, by direct contamination of the blood (as when virus-contaminated drug paraphernalia is shared), or by passage of the virus from an infected mother to her fetus or to a suckling baby. AIDS was first identified as a new infectious disease by the U.S. Centers for Disease Control and Prevention in 1981. See Appendix C, 1983, Montagnier and Gallo. HIV, lymphocyte, retroviruses.akinetic acentric (q.v.).
ala alanine. See amino acid.
akinetic acentric (q.v.).
ala alanine. See amino acid.
1. deficiency of chromoplasts in plants.
2. the inability to form melanin (q.v.) in the eyes, skin, and hair, due to a tyrosinase deficiency.
In hu-mans the condition is inherited as an autosomal re-cessive. Tyrosinase (TYR) is an essential enzyme for melanin synthesis, and some mutations in the tyrosi-nase gene (tyr) result in oculocutaneous albinism (OCA). The TYR gene is located in 11q14-21; it contains five exons, and its mRNA is 2,384 nucleo-tides long. More than 90 mutations have been iden-tified, most of the missense type. One such mutation in codon 422 results in the substitution of glutamine for arginine. The changed enzyme is heat-sensitive and so mimics the temperature-sensitive enzymes known for the Himalayan strains of mice, rabbits, and other species. See Himalayan mutant, ocular albi- nism, temperature-sensitive mutation, tyrosinase.
1. a plant lacking chromoplasts. 2. an ani-mal lacking pigmentation. See melanin. albomaculatus referring to a variegation consist-ing of irregularly distributed white and green regions on plants resulting from the mitotic segregation of genes or plastids.
albumin a water-soluble 70-kilodalton protein that represents 40-50% of the plasma protein in adult mammals. It is important both as an osmotic and as a pH buffer and also functions in the transport of metal ions and various small organic molecules. Al- bumin is synthesized and secreted by the liver. In the mouse the albumin gene resides on chromosome 5, separated from the alpha fetoprotein gene by a DNA segment about 13.5 kilobases long. In humans, these two genes are in the long arm of chromosome 4. See Appendix C, 1967, Sarich and Wilson; alpha fetoprotein.
alcaptonuria alkaptonuria (q.v.). alcohol any hydrocarbon that carries one or more hydroxyl groups. The term is often used to refer spe- cifically to ethyl alcohol, the product of yeast-based fermentations. Hereditary differences in alcohol preference are known to exist in mice. See Appendix C, 1962, Rodgers and McClearn.
alcohol dehydrogenase (ADH) a zinc-containing enzyme found in bacteria, yeasts, plants, and animals that reversibly oxidizes primary and secondary alco- hols to the corresponding aldehydes and ketones. In the case of yeast, ADH functions as the last enzyme in alcoholic fermentation. In Drosophila melanogas-
ter, ADH is a dimeric protein. By suitable crosses between null activity mutants it is possible to gener-ate heteroallelic individuals that exhibit partial res- toration of enzyme activity. This is often due to the production of a heterodimer with improved func-tional activity. The gene is of interest to develop-mental geneticist because its expression is controlled by two promotors. The proximal promotor lies adja-cent to the initiation codon and switches the gene on during the larval stage. The distal promotor lies 700 base pairs upstream and controls the production of ADH in the adult. See allelic complementation, promotor.
aldosterone an adrenal corticosteroid hormone that controls the sodium and potassium balance in the vertebrates.
aleurone the outer layer of the endosperm of a seed. Genes controlling the inheritance of aleurone color in maize provided early examples of epistasis (q.v.) and parental imprinting (q.v.). See kernel.
aleurone grain a granule of protein occurring in the aleurone.
Aleutian mink an autosomal recessive mutation in Mustela vison producing diluted pigmentation of the fur and eyes. The homozygotes show a lysosomal de- fect similar in humans to the Che´diak-Higashi syn- drome (q.v.).
alga (plural algae) any of a large group of aqua-tic, chlorophyll-bearing organisms ranging from sin-gle cells to giant seaweeds. See Appendix A: Cyano-bacteria, Dinoflagellata, Euglenophyta, Xanthophyta, Chrysophyta, Bacillariophyta, Phaecophyta, Rhodo-phyta, Gamophyta, Chlorophyta.
algorithm a set of simple mathematical proce-dures that are followed in a specified order to solve a problem in a finite period of time. Computers are instructed to perform tasks with programs contain- ing one or more algorithms.
alien addition monosomic a genome that con-tains a single chromosome from another species in addition to the normal complement of chromo-somes.
alien substitution replacement of one or more chromosomes of a species by those from a different species.
aliphatic designating molecules made up of linear chains of carbon atoms. aliquot a part, such as a representative sample, that divides the whole without a remainder. Two is an aliquot of six because it is contained exactly three times. Loosely used for any fraction or portion.
alkali metal any of five elements in Group IA of the periodic table: lithium (Li), sodium (Na), potas- sium (K), rubidium (Rb), and cesium (Cs). alkaline earth any element of Group IIA of the periodic table: beryllium (Be), magnesium (Mg), cal- cium (Ca), strontium (Sr), barium (Ba), and radium (Ra).
alkaline phosphatase an enzyme that removes 5′- P termini of DNA and leaves 5′-OH groups. The al- kaline phosphatase of E. coli is a dimer made up of identical protein subunits encoded by a single struc- tural gene. In vitro complementation was demon- strated using this enzyme. See allelic complementa- tion.
alkaloid any member of a group of over 3,000 cy- clic, nitrogenous, organic compounds, many of which have pharmacological properties. They occur mainly in plants, but are also synthesized by some fungi, amphibians, and arthropods. They include caffeine, cocaine, quinine, morphine, nicotine, reser- pine, strychnine, and theobromine.
alkapton 2,5-dihydroxyphenylacetic acid. See ho- mogentisic acid.