Genetically Controlled Variation

Inherited Variation. Genetically controlled variation in milk composition is evident from both interbreed and intrabreed studies. Some comparative studies of breed differences involve sampling from individual cows others use herd milk comparisons. Surveys with both kinds of sampling, summarized in Table 1.12, give a reasonably consistent picture of differences among breeds in the gross composition of milk. 

Fig. 1 Sources of variability in drug response in children. These include factors inherent to the child, the effect(s) of the disease being treated or other diseases, the effects of other therapies, ontogeny, and genetically controlled variation in drug disposition, action, and clearance...

Until recently the fatty acid composition of rapeseed oil was quite different from that of other edible vegetable oils from 40 to 60% of the fatty acid components of rapeseed oil consisted of the long chain fatty acids, erucic and eicosenoic. This unusual fatty acid composition has been the subject of numerous nutritional studies. Detrimental effects attributed to the long chain fatty acid components of rapeseed oil stimulated plant breeders to search for genetically controlled variation in these components. Rape plants which produce seed oil essentially without erucic acid were isolated (Ste-fansson et al., 1961) and this characteristic was incorporated into cultivars suitable for commercial production. The new "low erucic acid" rapeseed oils contain only the fatty acid components found in other edible vegetable oils traditionally used as food in the Western World. 

Due to the large variation in erucic acid content (0.1-60%) in the seed oils from rape and turnip rape, the separation of genetically controlled variation of erucic acid from environmental variation was relatively easy. The invariable association of substantial amounts of eicosenoic acid (e.g. 6%) with an allele for the presence of erucic acid which might condition the production of a low level of erucic acid (e.g., less than 2%) ensured selection of the genetically lowest level of erucic acid. 

Abstract Human body odour is individually specific and several lines of evidence suggest that to some extent it is under genetic control. There are however numerous other sources of variation, commonly labelled as environmental factors, which are the main aim of this paper. These include 1) reproductive status, 2) emotional state, 3) diet and 4) diseases. We primarily focus on axillary and genital odours as they have been proposed to have communicative function. We prelusively conclude that a specific diet and some diseases have major impact on variations in human body odour. 

In summarizing the material on anatomical variations, it may be pointed out that the observed variations encompass all structures, brain, nerves, muscles, tendons, bones, blood, organ weights, endocrine-gland weights, etc. Data are presented which show that these structures often vary tremendously from one individual to another and that their structural differences in general are under genetic control. 

The genetotrophic idea was first conceived in connection with the experimental work on alcohol consumption by rats. When it was found that the alcohol consumption of rats (1) was highly individual 12, 13, 14 (as were also their excretion patterns), 15 and (2) was genetically controlled (as evidenced by the distinctive behavior of each inbred strain and the relatively small variation within inbred strains),13, 14 and (3) could be increased by deficient diets and abolished by fortified ones, 12, 13 the genetotrophic ideas appeared to be the only reasonable interpretation of the facts. 16,17 Since these original observations were made, dozens of other facts, many of which have been and will be presented in the present volume, have become explicable on the basis of the genetotrophic concept. To date there are no observations, so far as I am aware, that appear to go counter to this idea. 

The chemical composition of a glandular secretion may vary considerably between species. Very little is known yet on such differences in vertebrates, where known, it is not clear whether the differences are genetically controlled, the result of different diets or other ecological or phenotypical variation, or, finally, a combination of different factors. 

Toxicologists should also consider making more use of the mouse instead of the rat. They are less costly to maintain, use less test substance, there are many inbred and genetically modified strains, and it is easier to identify gene loci controlling variation in response to xenobiotics in this species. 

Atlas SA, Vesell ES, Nebert DW. Genetic control of interindividual variations in the inducibility of aryl hydrocarbon hydroxylase in cultured human lymphocytes. Cancer Res 1976 36(12) 4619-4630. 

We have discussed both target receptors and pharmacokinetics in this book. Protein manufacture is under direct genetic control, and two factors are of particular relevance here. First, the precise structure and function of protein macromolecules (receptors) targeted by a specific drug molecule will vary in different individuals. Since the structure and function of the protein are directly related to how the drug molecule will interact with that protein, individuals responses to the drug will vary. Second, there are genetic variations in metabolic enzymes (proteins) and hence metabolism. Both of these processes fall neatly into the domain of pharmacoproteomics (see Section 14.8). 

KLIEBENSTEIN, D.J., KROYMANN, J., BROWN, P., FIGUTH, A., PEDERSEN, D., GERSHENZON, J., MITCHELL-OLDS, T., Genetic control of natural variation in Arabidopsis glucosinolate accumulation., Plant Physiol., 2001,126, 811-825. 

Gupta, R.B., Shepherd, K.W. (1990). Two step one dimensional SDS-PAGE analysis of LGM subunits of gjutenin. 1- Variation and genetic control of the subunits in hexaploid wheats. Theor. Appl. Genet., 80, 65-74. 

Genetic Variation. The concentration of many individual nutrients in foods of plant origin is under genetic control. Baker (34) reviewed some examples of genetic manipulation that improved the quantity of )3-carotene in tomatoes, methionine in beans, and lysine in com. Variations of ascorbic acid content of different varieties of raw vegetables and fruits is notoriously high (35). Twofold variation in vitamin C concentration in different strains of a vegetable or a fmit is common and a fivefold variation can be found. Differences in ascorbic acid contents (35- to 300-fold) of different strains of a fmit were reported prior to 1950 (36). These reports have not been substantiated. 

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