| balanced lethal system | <genetics> A population with non-linked, recessive alleles of a gene, where an individual who has two copies of the recessive allele and is therefore homozygous is dead, while an individual who has only one copy of it, and one copy of a different allele (and is heterozygous) survives. (09 Oct 1997) |
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| genes, lethal | Genes which result in the premature death of the organism; dominant lethal genes kill heterozygotes, whereas recessive lethal genes kill only homozygotes. (12 Dec 1998) |
| genetic lethal | A disorder that prevents effective reproduction by those affected; e.g., Klinefelter syndrome. (05 Mar 2000) |
| granuloma, lethal midline | A non-neoplastic disease of unknown aetiology beginning with inflammation, ulceration, and perforation of nose and palate and progressing to gradual destruction of midline facial structures. (12 Dec 1998) |
| chicken embryo lethal orphan virus | <virology> A virus with characteristics of adenovirus, and similar to quail bronchitis virus. Synonym: chicken embryo lethal orphan virus. (05 Mar 2000) |
| minimal lethal dose | <pharmacology> The minimal dose of a toxic substance or infectious agent that is lethal, as assayed in various experimental animals (e.g., the least amount of diphtheria toxin that, on an average, kills a 250-g guinea pig within 96 hours after subcutaneous inoculation). When followed by a subscript (generally "MLD50"), denotes the minimal dose that is lethal to a certain percentage (e.g., 50%) of animals so assayed, LD05. See: lethal dose. (05 Mar 2000) |
| clinical lethal | A disorder that culminates in premature death. (05 Mar 2000) |
| conditional-lethal mutant | A viral mutant that can replicate under some (permissive) conditions but not under other (restrictive or nonpermissive) conditions, the parent (wild type) strain being able to replicate under both conditions. See: suppressor-sensitive mutant, temperature-sensitive mutant. Synonym: conditional-lethal mutant. (05 Mar 2000) |
| conditionally lethal mutant | A viral mutant that can replicate under some (permissive) conditions but not under other (restrictive or nonpermissive) conditions, the parent (wild type) strain being able to replicate under both conditions. See: suppressor-sensitive mutant, temperature-sensitive mutant. Synonym: conditional-lethal mutant. (05 Mar 2000) |
| 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) |
| y-suppressed lethal gene | <genetics> In the fruit fly Drosophila, this is a recessive, lethal gene that kills XO flies but not normal XY male flies. (09 Oct 1997) |
| zygotic lethal gene | <genetics> A mutated or otherwise defective gene at embryonic or larval stages. (06 May 1997) |
| lethal | Deadly, fatal. Origin: L. Lethalis, from lethum = death (18 Nov 1997) |
| lethal coefficient | <microbiology> That concentration of disinfectant that kills bacteria at 20-25캜 in the shortest period of time. (05 Mar 2000) |
| lethal dose | <pharmacology> The amount, or dosage, of a toxin necessary to cause death. (16 Mar 1998) |