| clonal | Pertaining to a clone. (05 Mar 2000) |
|---|---|
| clonal aging | The deterioration in successive generations of a clone; thus paramecia and other simple forms, if allowed to reproduce asexually for a number of generations, invariably undergo deterioration, the characters of each group of descendants progressively departing from those of the original sexually produced ancestor. (05 Mar 2000) |
| clonal anergy | Functional inactivation of t- or B-lymphocytes rendering them incapable of eliciting an immune response to antigen. This occurs through different mechanisms in the two kinds of lymphocytes and can contribute to self tolerance. (12 Dec 1998) |
| clonal deletion | The removal of B-cell and T-cell varieties which recognise parts of the organisms body as targets of the immune system. This process naturally occurs early in the organisms development so that the organism will not be autoimmune (having an immune reaction against one's own body tissues) later in life. (09 Oct 1997) |
| clonal deletion theory | The elimination of certain T-cell populations in the thymus that have receptors for self-antigens. See: immunologic tolerance. (05 Mar 2000) |
| clonal expansion | Production of daughter cells all arising originally from a single cell. (05 Mar 2000) |
| clonal selection | <cell biology> The process whereby one or more clones, i.e. Cells expressing a particular gene sequence are selected by naturally occurring processes from a mixed population. Generally the clonal selection is for general expansion by mitosis, particularly with reference to B lymphocytes where selection with subsequent expansion of clones occurs as a result of antigenic stimulation only of those lymphocytes bearing the appropriate receptors. (18 Nov 1997) |
| clonal selection theory | A theory which states that each lymphocyte has membrane bound immunoglobulin receptors specific for a particular antigen and once the receptor is engaged, proliferation of the cell occurs such that a clone of antibody producing cells (plasma cell) is produced. (05 Mar 2000) |
| biologic evolution | Biologic evolution was contrasted with cultural evolution in 1968 by A.G. Motulsky who pointed out that biologic evolution is mediated by genes, shows a slow rate of change, employs random variation (mutations) and selection as agents of change, new variants are often harmful, these new variants are transmitted from parents to offspring, the mode of transmission is simple, complexity is achieved by the rare formation of new genes by chromosome duplication, biologic evolution occurs with all forms of life, and the biology of humans requires cultural evolution. See Cultural evolution. (12 Dec 1998) |
| chemical evolution | The theory of the process by which life arose from inorganic matter. (05 Mar 2000) |
| coincidental evolution | <molecular biology> The tendency for the same mutation to arise simultaneously in all copies of a gene which has been duplicated. (09 Oct 1997) |
| concerted evolution | The ability of two related genes to evolve together as though constituting a single locus. Synonym: coincidental evolution. (05 Mar 2000) |
| convergent evolution | The process where two unrelated structures in unrelated organisms evolve to perform similar functions. (The structures are called analogous structures.) For example: the wings of bats, birds, and insects evolved separately from each other but all are used to perform the function of flying. For another example: the complex eyes of vertebrates, cephalopods (squid and octopus), cubozoan jellyfish, and arthropods (insects, spiders, crustaceans) evolved separately, but all perform the function of vision. (09 Oct 1997) |
| cultural evolution | The continuous developmental process of a culture from simple to complex forms and from homogeneous to heterogeneous qualities. (12 Dec 1998) |
| saltatory evolution | The theory that evolution of a new species from an older one may occur as a large jump, such as a major repatterning of chromosomes, rather than by gradual accumulation of small steps or mutations. Compare: emergent evolution. (05 Mar 2000) |