Heritability definition

W. T., Springer, T. A. (1985). The severe and moderate phenotypes of heritable Mac-1, LFA-1 deficiency Their quantitative definition and relation to leukocyte dysfunction and clinical features. J. Infect. Dis. 152,668-89. 

The definition of resistance provided by Prichard et al. (1 980) is suitable for trematodes and cestodes. Resistance is present when there is a greater frequency of individuals within a population able to tolerate doses of compound than in a normal population of the same species and is heritable. The definition has been refined for Schistosoma sp. to stress the difference between tolerance and resistance. Tolerance is when a drug has never worked against a parasite, e.g. oxamniquine and S. japonicum. Genes for resistance are present if an isolate of a parasite is significantly less susceptible than the most susceptible isolate of the same species (Coles and Kinoti, 1997). 

The biologic processes described above and cytosine methylation, fit the epigenetic definition well because they are heritable. However, whether the entire repertoire of histone modifications is heritable remains to be established. In fact, it is likely that only a subset will have epigenetic inheritance. 

There were also some observational foreruimers. In 1932, Snyder (3) described a heritable disability of some people to taste phenylthiocarbamide. In 1943, Savin and Glick (4) noticed a genetic lack of atropine esterase in some rabbits these animals died while eating belladoima leaves, whereas most rabbits were not affected. These cases were perceived as isolated observations they preceded the definition of pharmacogenetics but they helped later investigators to establish pharmacogenetics as a science. 

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