Íslenskar landbúnaðarrannsóknir - 01.03.1970, Side 107

Íslenskar landbúnaðarrannsóknir - 01.03.1970, Side 107
COLOUR INHERITANCE IN ICELANDIC SHEEP 105 agouti. The fox-red lamb has alrnost cer- tainly been tan-coloured and probably the agouti lamb as well. One can assume that the coffee-brown ewes were homozygous for recessive brown and that the black Karakul ram was heterozygous for recessive bron. If the ram and some of the coffee-brown ewes were heterozygous for the intensifier, all the Fx’s not carrying the intensifier would be expected to become white or tan, assuming the gene for white to be present. The incomplete dominance of dominant brown over white reported by Bonikowsky (1935) and indicated by Duck (1921, 1922), Vasin (1928) and Luthge (1932, quoted by Serra, 1948) is further evidence of its great similarity to the tan colour. As described earlier the tan colour in the Icelandic sheep shows great variation. D. WHITE COLOUR WITH OR WITHOUT TAN As white is the most frequent sheep colour, most investigations regarding colour in- heritance in sheep have used white as a standard, and the characters studied liave often been termed dominant and recessive on basis of their behaviour in heterozvgotes obtained in crosses with white sheep. This does not necessarily indicate an allelic rela- tionsliip of the colours studied to the white colour. White may occur as the fleece colour only, with pigmented extremities as for example in many of the British Down breeds, or may extend to the colour on head and feet, with no pigment visible, as in some extreme white-faced breeds such as the Merino and the Dorset Horn. There is general agreement that white colour is produced by a single gene, epistatic to re- cessive black and recessive brown. Some ex- ceptions to this rule have been found (for review, see Brooker and Dolling, 1965). The exceptions can usually be explained by the occurrence of faulty parentage or difference in definition of white colour. The inheritance of the tan colour under that name has not been studied as far as the writer is aware of except in his own work, frorn which some preliminary results have been published (Adalsteinsson, 1965). The results showed that selection against tan colour gave a very rapid response. E. PATTERNS AND ABSENCE OF PATTERNS IN NONWHITE SHEEP 1. Badgerface and mouflon The inheritance of the badgerface patt- ern was studied simultaneously by Roberts (1924) and Wriedt (1924), the latter calling the pattern “gromet”. Their conclusion was that badgerface was recessive (or hypostatic) to white. 7’hey both observed a consider- able variation in the pattern. Roberts (1924) found tliat the badgerface pattern was not exhibited iu the presence of do- minant black. Roberts and White (1930 a) further showecl the badgerface pattern to be dominant (or epistatic) to recessive black, a result which was confirmecl by Berge (1958, 1964 a). Roberts and Jenkin (1926) describecl the mouflon pattern, wliich they terrned revers- ed badgerface. Roberts (1928) postulated that the genes for white, badgerface, mou- flon and black might be allelic, white being dominant to all the others, badgerface clo- minant to mouflon and black, and mou- flon dominant to black. This hypothesis was abandoned, how- ever, in furher experiments, where the in- heritance of white, recessive black, reces- sive brown, badgerface and mouflon was studied simultaneously (Roberts and White, 1930 a), on the following grounds. White — recessive brown F2 was found to give some black-pigmented lambs, which would not occur if the genes for white, black and brown were alleles.
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