Íslenskar landbúnaðarrannsóknir - 01.03.1970, Side 103

COLOUR INHERITANCE IN ICELANDIC SHEEP 101
sires in the present study which show segre-
gation at two loci simultaneouslv, but
where the origin ol the alleles is not
known. The groups of progeny are too
small, however, to be of much value in an
attempt to establish presence or absence of
linkage by tests of heterogenity.
CHAPTER VIII
Discussion of inheritance of colour in sheep
In the following, earlier investigations on
the inheritance of the colours encountered
in the present study will be discussed, i.e.
recessive black and brown pigment in non-
white sheep, white colour with or without
tan, the colour patterns grey, badgerface,
mouflon, grey mouflon and no pattern,
and the presence or absence of white mark-
ings. In addition the relation of dominant
black and brown to the above colours will
be discussed. The literature on these aspects
of colour inheritance in sheep has been re-
viewecl by Rae (1956), Rendel (1957),
Berge (1958, 1964 a), Ryder and Stephen-
son (1968) and Searle (1968).
A. RECESSIVE BLACK VS. RECES-
SIVE BROWN PIGMENT
Roberts and White (1930 a), studying the
inheritance of recessive black and recessive
brown in the Shetland and Soay sheep (as
contrasted to white), came to the conclus-
ion that the brown pigment was recessive
(or hypostatic) to black. Zóphóníasson
(1934) and Berge (1958) arrived at the same
conclusion for Icelandic and Old Norweg-
ian sheep, respectively. In all these cases,
there was no difficulty in distinguishing
between black and brown pigment. Serra
on the other hand, postulated three allelic
genes for brown pigment, all recessive or
hypostatic to black. Vasin (1928) found a
recessive dark brown colour, which he as-
sumes to be diluted black, in both the
northern shorttailed sheep of Russia and
in nonwhite Merinos. It is not certain
whether this is the same brown as found
in the Shetland, Soay, Icelandic and Old
Norwegian sheep. Robf.rts and White
(1930 b) describe a recessive bleaching of
clominant black to brown, but as this
bleaching is not present at birth it is rnost
likely different from Vasin’s (1928) brown.
Roberts (1932), describing the colour of
the wild Mouflon and its inheritance, con-
cluded that the undercoat of the Mouflon
was clearly a brown, but the wild Mouflon
was shown to carry genes for black pig-
ment, so the brown colouring of the under-
coat of the wild Mouflon rnust be due to
a dilution of black. Ewart (1919) crossed
sheep from Russia, called Siberian Mou-
flon, witli Cheviot. The Fx was white, and
a backcross of brown F2 females to the
Siberian Mouflon ram gave purebreeding
brown. It seerns likely fronr Ewart’s experi-
ments that the brown colour in these cross-
es is the same as the recessive brown in the
Shetland and Soay sheep. This would imply
that the Cheviots used in the experinrent
also carried tlre recessive brown.
Roberts and White (1930 a) state that
tlre exact genetic relationship between
black and brown cannot be established, as
long as genes lower in the series, i.e. reces-
sive to brown, are not discovered. Berge
(1964 a) on the other hand, assumes that
brown is produced by a honrozygous reces-
sive gene which converts black pigment in-