| lethal dwarfism | Dwarfism leading to intrauterine or neonatal death. (05 Mar 2000) |
|---|---|
| lethal equivalent | A combination of selective effects that on average have the same impact on the composition of the gene pool as one death; e.g., two carriers at 50% risk of dying would be the lethal equivalent of one carrier at 100% risk, in the population genetics of recessive traits lethal equivalent is expressed as twice the sum of the expected number of deaths ascribable to the genetic load. Expression used of the genetic load of recessive genes in heterozygous state that if in homozygous state would cause death or carry a risk of death. The expected number of deaths from all such genes is expressed in lethal equivalent. (05 Mar 2000) |
| lethal factor | A disorder that prevents effective reproduction by those affected; e.g., Klinefelter syndrome. (05 Mar 2000) |
| lethal gene | A gene that produces a genotype that leads to death of the organism before reproduction is possible or that precludes reproduction; for a recessive gene the homozygous or hemizygous state is lethal. (05 Mar 2000) |
| lethal midline granuloma | Destruction of the nasal septum, hard palate, lateral nasal walls, paranasal sinuses, skin of the face, orbit and nasopharynx by an inflammatory infiltrate with atypical lymphocytic and histiocytic cells; presumably a form of lymphoma in most cases. An obsolete term for polymorphic reticulosis. Synonym: granuloma gangrenescens, malignant granuloma, midline malignant reticulosis granuloma. (05 Mar 2000) |
| lethal mutation | <genetics, molecular biology> Mutation that eventually results in the death of an organism carrying the mutation. (18 Nov 1997) |
| genetic | <biology> Pertaining to reproduction or to birth or origin. (07 May 1998) |
| genetic amplification | A process for producing an increase in pertinent genetic material, particularly for increasing the proportion of plasmid DNA to that of bacterial DNA. Includes the production of extrachromosomal copies of the genes for RNA. (05 Mar 2000) |
| genetic assimilation | <genetics> A situation in which a characteristic that is normally expressed only in certain environmental situations becomes fixed in a population so that it no longer requires environmental factors to be expressed. (07 May 1998) |
| genetic association | The occurrence together in a population, more often than can be readily explained by chance, of two or more traits of which at least one is known to be genetic. (05 Mar 2000) |
| genetic block | <biochemistry, molecular biology> An obstruction in a biochemical pathway caused by a mutation that has crippled production of an enzyme critical to the pathway. (07 May 1998) |
| genetic burden | The genetic debt due to harmful mutation but as yet undischarged. (In a large population of fixed size every mutation with diminished genetic fitness will eventually become extinct and depending on the details of inheritance and phenotype must be paid for by a fixed number of genetic deaths per mutation, the genetic debt.) (05 Mar 2000) |
| genetic carrier | An unaffected heterozygote bearing a usually harmful recessive gene, a cancer that bears a dominant but latent age-dependent trait to have offspring with unbalanced karyotypes. (05 Mar 2000) |
| genetic code | <molecular biology> Relationship between the sequence of bases in nucleic acid and the order of amino acids in the polypeptide synthesised from it. A sequence of three nucleic acid bases (a triplet) acts as a codeword (codon) for one amino acid. (18 Nov 1997) |
| genetic colonisation | <molecular biology> The process of a parasite (such as a virus) inserting genes into a host's genome which cause the host cell to synthesise products that are only useful to the parasite. (07 May 1998) |