Animal genetics / Frederick B. Hutt.

  • Frederick Hutt
Date:
[1964]
Catalogue details

Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Animal genetics / Frederick B. Hutt. Source: Wellcome Collection.

    481/578 page 459
    BIOCHEMICAL GENETICS 459 in Holstein-Friesians in the United States; and in Jamaica Reds and Jamaica Blacks. It is transmitted in cattle as an autosomal recessive trait. In pigs, porphyria has been found in New Zealand and in Den¬ mark. The condition may not be biochemically the same as in cattle, for its onset is delayed somewhat, and the affected pigs are appar¬ ently not photosensitive, as are the cattle. All the Danish cases were descended from a single boar. Porphyria in swine is transmitted as a dominant trait, but it is not yet clear that a single gene is re¬ sponsible. Excessive Phylloerythrin in Sheep Photosensitivity of a different kind from that caused by porphyria in cattle was studied in Southdown sheep by Clare and Hancock in New Zealand. In afflicted lambs, the liver fails to excrete phylloerythrin, which is a product of the digestion of chlorophyll. All of them are normal at birth and have no difficulty until they begin to graze at five to seven weeks. The severity of their injuries after that age varies according to the intensity of light and the proportion of their diet that comes as milk from the ewe ( with the remainder from grass ). If the lambs are left outdoors, they develop eczema over the face and ears (Fig. 20-4), and death ensues within two to three weeks after the appearance of the first symptoms. On the other hand, if the lambs are kept indoors during the day, and allowed out only at night, they learn to do their grazing at night, to keep out of the sun during the day, and so to survive despite their abnormal physiology. In genetic studies with these sheep, Hancock found both sexes to be equally affected, and ratios in the different matings were as follows : Offspring Parents Normal Affected Homozygous normal X affected 74 0 Heterozygotes X affected 18 16 Affected X affected 0 14 From these unusually good numbers for animals as big as sheep, it is clear that this abnormality of metabolism is a simple, autosomal, recessive character. Although it has not yet been found in other animals, the possibility should not be overlooked that some of the photosensitization commonly caused by the eating of certain plants might be aggravated in some animals by genetic variations in ability to break down the sensitizing pigments that those plants contain.
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