Based on 17 118 observations of colour type in lambs, 3 pigment types were found: tan, black and brown. White sheep either lack pigment or have tan pigment. Non-white sheep have either black or brown pigment, and this is sometimes accompanied by tan. Four colour patterns are known in non-white sheep: grey, badger-face, mouflon and grey mouflon. The patterns are independent of whether the pigment is black or brown. Altogether 17 main colours are possible. Broken colour in non-white sheep is expressed independently of pigment type and pattern. Colour genes are found at 3 loci, A, B and S. Of the alleles at the A locus, A1, A6, A2, A3 and A5 give rise to the colours or patterns white, grey mouflon, grey badger face, mouflon and no pattern resp. Inhibition of pigment is dominant to pigment production. At the B locus, 2 alleles for pigment production are known: B1 (dominant) giving black pigment and B2 (recessive) producing brown pigment. Two alleles are known at the S locus, S1 (dominant) giving unbroken colour, and S2 (recessive) giving broken colour. No linkage has been found between the 3 loci. The presence of the A1 allele decreased ewe fertility considerably, and some deviations in segregation could be explained in terms of selective embryonic mortality. The agreement between results of the present work and previous results reported in the literature is discussed and related to colour inheritance in rodents.S. Adalsteinsson.
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