Linkage disequilibrium

The condition in which two genes are close enough together on a chromosome that it is not likely that they will be separated by recombination during meiosis.

Linkage analysis

A means of statistically correlating phenotype with genotype using lod scores.

Lod score

The ratio of the likelihood of two or more loci remaining together when chromosomes recombine (true linkage) to the likelihood of chance alone.

Lowest-observed-adverse-effect level (LOAEL)

The lowest exposure level at which there are statistically or biologically significant increases in the frequency or severity of adverse effects in the exposed population and its appropriate control.


Margin of exposure (MOE)

The ratio of the NOAEL to the estimated exposure dose.

Maximum tolerated dose (MTD)

The maximum dose that an animal species can tolerate for a major portion of its lifetime without significant impairment or toxic effect other than carcinogenicity.

Mechanism of action

The detailed molecular knowledge of the events that result in an adverse developmental response in an organism. This knowledge includes the following types of mechanistic information: (1) The toxicant’s kinetics and means of absorption, distribution, metabolism, and excretion within the mother and conceptus; (2) Its interaction (or those of a metabolite derived from it) with specific molecular components of cellular or developmental processes in the conceptus or with maternal or extraembryonic components of processes supporting development; (3) The consequences of the interactions on the function of the components in a cellular or developmental process; (4) The consequences of the altered process on a developmental outcome, namely, the generation of a defect. See also ‘mode of action.’

Mendelian trait

Phenotype that shows simple pattern of inheritance. Mendelian traits are usually governed by a single genetic locus.

Mendelian gene

A gene located in a chromosome that obeys the laws of Mendelian inheritance.



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