Íslenskar landbúnaðarrannsóknir - 01.03.1970, Blaðsíða 104

102 ÍSLENZKAR LANDBÚNAÐARRANNSÓKNIR
to brown, i.e. that brown sheep are homo-
zygous black as well as homozygous for this
recessive conversion gene. This assumption
is based on the finding of a high propor-
tion of black and multicoloured fibres in
the fleece of a brown (red) ram of the Old
Norwegian breed (Berge 1964 b).
In light of the available literature, there
seems no reason to assume that the genetic
relationship between black and brown pig-
ment in earlier studies differs from that
found in the present study.
Several other authors have studied the
occurrence and inheritance of recessive
black in sheep (as contrasted to white), but
it seems almost certain that their black
sheep have consisted of several types of
nonwhite animals. Among these are Kelley
and Shaw (1942), Kelley (1943), Hayman
and Cooper (1964, 1965) and Brookf.r and
Dolling (1965). AU these authors conclude
that the nonwhite condition is recessive to
white.
Kelley and Shaw (1942) defined the
nonwhite colour in a different way from
what has been done in the present study.
Their white group consisted only of ani-
mals which showed no obvious large patch
of pigmented wool. Animals with an ob-
vious patch of black wool, but otherwise
white were classified as pigmented.
The results obtained by Warwick et. al.
(1957) on the inheritance of recessive black
are worth special attention in this connec-
tion. They postulatecl that recessive black
could be produced by two pairs of genes,
any one of which, when homozygous, would
give recessive black. Their results have
been quoted widely in the literature and
they have been used to explain the occurr-
ence of white lambs from matings where
both parents were nonwhite.
Because these results are not supported
by the results from the present study, they
have been examined carefully, and it seems
that an alternative interpretation is poss-
ible, as far as the results from the Ram-
bouillet X Mouflon crosses are concerned.
The crucial matings are given on p. 103
together with the assumed genotypes of the
animals involved, using both interpreta-
tions of inheritance.
All the evidence from ram No. 603-S10
thus sugg’sts that he has shown tan colour
and has been of genotype AXA4. When the
data are interpreted in this way the results
agree fully with the results of the present
study. The occurrence of the black badger-
face-mouflon lamb (Fig. 4B) gives also a
valuable support to the findings of the
present study that the patterns badgerface
and mouflon will both be expressed when
they occur together in the same animal.
The report does not permit any alterna-
tive interpretation of the oher case where
two pairs of genes for recessive black were
found. That assumption is based on the
occurence of two black lambs where none
were expected. It is clear from the report
that the definition of black colour has been
widely different from that used in most
studies on colour inheritance in sheep.
These two lambs can therefore hardly be
taken as a proof of the existence of two
pairs of genes which can produce recessive
black.
B. DOMINANT BLACK
The dominant black is indistinguishable
from recessive black (Vasin 1928, Roberts
and White 1930 b). It is generally assumed
that dominant black is produced by an
intensifying gene which suppresses com-
pletely the inhibiting action of the gene
for white and the pattern genes on pig-
ment production. The gene for dominant
black does not suppress the action of the
genes for white markings (for references see
Berge, 1964 a).
It has been demonstrated by Vasin
(1928), Roberts and White (1930 a) and