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L’homologie entre l’Homme et les autres Mammifères pour les loci de coloration du pelage

Abstract : Few research workers have studied the homology between coat color loci in Man and in the other Mammals, although A, B, C, D, E and particularly P, are well known in the latter. This lack of interest is the result of some masking of the action of such genes because Man is an alopecic animal, that is, he has no hairy coat in which mutant action at the usual loci is clearly distinguishable. Since the coat has disappeared, skin coloration has developed primarily to protect against the radiations of the sun and mainly against U.V. Man has been found in high intertropicai savannah zones. Weak, cumulative, not very highly specialized variants of this protection by skin melanin probably occurred, short-circuiting major mutants which might have appeared at the usual loci. Afterwards, an adaptative change in tegument took place in some populations which had migrated northwards : demelanization. The melanin layer, which had been useful at low altitudes, prevented the U.V., which had become rare, from passing through the skin to activate provitamin D synthesis, and rickets resulted. This adaptative change presented an unusual, complex situation in a mammalian species, and the present formula, using basic loci (A, Agouti and E, Extension) for the alternative synthesis of eu- and phaeomelanin, is still be only indicative : aaE+E+ or A?A?EdEd for dark as well as for mongoloid races and most whites which are not red-haired, the latter being AyAy E+E+ or aa ee or A?A? ee. The other color loci which have mutated do not seem to have produced any mutants to adapt the species either to the usual loci (in D, Dilution, with phenylketonuria, or better delute lethal, and in C, True albinism, with albino mutants which have not yet been definitively localized) or to more unusual loci reported in mammals but where color variation is accompanied by serious abnormalities such as Chediak-Higachi disease or Waardenburg syndrome. These mutants are maintained at a low frequency level by genetic drift, heterozygote advantage or the founder effect. The analysis of skin color by methods of quantitative genetics sometimes gives contradictory results which indicate that near the polygenes may be genes with greater effects. This may be proved, at least in some cases, using histological and histochemical methods.
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J.J. Lauvergne. L’homologie entre l’Homme et les autres Mammifères pour les loci de coloration du pelage. COLLOQUE INRA-INSERM. Génétique de la pigmentation de l'homme comparée à celle des autres mammifères, Jan 1980, Jouy-en-Josas, France. ⟨hal-02853994⟩

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