| mendelian trait | A categorical trait that segregates in accordance with a single-locus genetic system. (05 Mar 2000) |
|---|---|
| chromosomal trait | A trait dependent on a recurrent chromosomal aberration. (05 Mar 2000) |
| codominant trait | See: codominant. (05 Mar 2000) |
| selectable marker | <molecular biology> A gene whose expression allows one to identify cells that have been transforrned or transfected with a vector containing the marker gene. (09 Oct 1997) |
| sickle cell trait | <haematology> This condition occurs in people who have one of two possible genes (i.e., they are heterozygous forthe allele) that code for the defective haemoglobin responsible for sickle cell anaemia. The coditionis diagnosed by exposing an individual's red blood cells to a low oxygen environment, if the trait is present, the cells will turn to a sickle shape. People with this trait may suffer milder symptoms of sickle cell anaemia, or may have no symptoms. Some scientists believe the trait actually provides an evolutionary advantage in tropical environments because the slightly altered shape of the blood cells causes a person to be more resistant to malaria. (09 Oct 1997) |
| hypoxanthine-guanine phosphoribosyl tranferase marker | The gene which codes for the enzyme hypoxanthine-guanine phosphoribosyl transferase. It is a selectable marker because cells which have a defective version of this gene are resistant to poisoning by toxic purine derivatives which result from the metabolic pathway that the HGPRT enzyme catalyses. (The purine derivatives are toxic because they incorporate into DNA as a result of the HGPRT enzyme's actions). Because the defective gene cannot produce the enzyme, no toxic purine derivatives are produced, the gene can therefore be selected for. (09 Oct 1997) |
| nonpenetrant trait | A genetic trait that is not phenotypically manifest because of non-genetic factors it therefore does not include recessivity, epistasis, hypostasis, or parastasis but does include environmental factors and pure random effects such as lyonization. (05 Mar 2000) |
| surrogate marker | <biology> A laboratory measurement of biological activity within the body that indirectly indicates the effect of treatment on disease state. CD4 cell counts and viral load are examples of surrogate markers in HIV infection. (19 Jan 1998) |
| dominant lethal trait | Trait, expressed in the phenotype if present in the genotype, that precludes having descendants. All such cases are necessarily sporadic and must represent new mutations as the usual methods of classical genetics provide no means of demonstrating any genetic component whatsoever, except for tenuous arguments such as advanced paternal age. Molecular biology may help although the methods may be tedious; if there is an epistatic gene that may mask the trait, the logic is more tractable, though complex. (05 Mar 2000) |
| dominant trait | An outstanding mental or physical characteristic. See: dominance of traits. (05 Mar 2000) |
| qualitative trait | <genetics> A feature that can conveniently and effectively be analyzed by sorting into classes either because there is no satisfactory way of measuring it (as with blood groups) or because it falls into natural classes so that the variation among classes far exceeds that within classes (e.g., the phenotypic effects of many enzyme polymorphisms); existence of categories suggests but does not prove the operation of a major, simple, underlying cause. Synonym: qualitative trait. (05 Mar 2000) |
| quantitative trait | A characteristic showing quantitative inheritance such as skin pigmentation in man. (12 Dec 1998) |
| intermediate trait | A measurable trait in which there is some evidence of the operation of a simple major cause, but in which the variation within the putative categories is such as to cause overlap and hence ambiguity in classification of any particular reading. (05 Mar 2000) |
| oncofetal marker | A tumour marker produced by tumour tissue and by foetal tissue of the same type as the tumour, but not by normal adult tissue from which the tumour arises. (05 Mar 2000) |
| threshold trait | A trait that falls into natural groups that originate not in categorically distinct causes but in whether or not the outcome attains critical values; e.g., gallstones may result from a categorical cause or from unusual levels of causal factors that themselves show no evidence of grouping. Synonym: liminal trait. (05 Mar 2000) |