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.