Dr. Searle has provided an important synthesis of the results of genetic research on coat colour, and has covered all mammals for the first time in one very readable volume. Those who work with farm animals, and feel the neglect of coat colour studies, will be envious of the details achieved by workers with small mammals that breed more readily and can be kept in larger numbers.
The treatment starts with a useful summary of inheritance in mammals including mutations and gene function, although colour is inherited almost entirely through major genes segregating in Men-delian fashion. Indeed, had the laws of inheritance not been discovered with peas it is possible that they would have been discovered with coat colour, because good Mendelian ratios can be obtained with many of the genes responsible for coat colour. Next covered are methods of comparative genetics, and gene action, transplantation experiments between rats and mice having provided evidence of the homology of colour genes between species.
The book continues with an interesting account of the nature and function of the coat and its colour. The mammalian colour range is: white-grey-black-brown-yellow-orange-red, and one of its functions in the wild state is to communicate either mating desires or warning signals to other animals. It also functions in concealment, and so colour is very important in adaptation.
There is a useful description of colour production at the cellular and biochemical level before the different coat colour genes, and their action, are detailed. The allelic series responsible for colour are as follows: (A) Agouti, named after the banded hairs found in the wild type, is found in many groups, and probably the wild sheep, but the situation in cattle is not clear. Brown (B), in which black is dominant to brown, is found in Soay and Shetland sheep, but not in cattle or pigs. The Albino series (C) reduces colour intensity by reducing the number of pigment granules; it does not appear to occur in sheep and pigs, but may do so in cattle.
Dilute (D) makes pigment appear grey by clumping the granules, but this does not exist in cattle or sheep. Adalsteinsson (1960) in Iceland [see A.B.A., 30, No. 1823] and Berge (1958 and 1964) in Norway [see A.B.A., 27, No. 286 and 33, No. 2483] have proposed alternative ways for the inheritance of the grey of sheep in papers that have apparently been missed in this very wide coverage of the literature. Extension series (E) extends or diminishes pigmentation, and this apparently does occur in cattle, sheep and pigs. Finally, another pigment-reducing series, Pink-eyed (P), can only be demonstrated with certainty in rodents.
There are chapters on different mammalian groups-rodents, lagomorphs, carnivores, ungulates, and all the other orders, including monotremes, marsupials and man. Variegated colours and pathology are covered, and the book ends with an excellent evolutionary synthesis which shows that the author is aware of the pitfalls of projecting the findings from one order of animals to other, less studied, orders. But Dr. Searle claims that more is known about mammalian colour genetics than about any other character in any animal group, and suggests that colour could contribute more to an understanding of evolution if the remaining gaps in our knowledge were to be filled. M. L. Ryder.
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