Íslenskar landbúnaðarrannsóknir - 01.03.1970, Síða 112

1 I 0 ÍSLENZKAR LANDBUNAÐARRANNSÓKNIR
also found in the Icelandic sheep, and
in nonwhite Merinos (Henseler, 191B;
Davy, 1927; Roberts, 1926; Adametz,
1917; Pálsson, 1944; Hayman and
Cooper, 1964).
4. Persian hooded. This colouration,
which gives a black head and neck
and white body, is common among
Asian and African fattailed sheep,
where it occurs in combination with
dominant black. A similar type of
markings is sometimes found in non-
white Icelandic sheep. (Henseler,
1913; Vasin, 1928; Davy, 1927; Páls-
son, 1944).
5. A white collar. This occurs in some
Russian breeds of sheep, and is found
both in connection with dominant and
recessive black. A similar type of collar
usually occurring in sheep with wliite
head spot or blaze and white on the
feet has also been described in Ice-
landic sheep (Vasin, 1926; Pálsson,
1944).
Berge (1964 a) follows in general Vasin’s
(1928) interpretation of the inheritance of
these five groups of markings assigning the
following gene action and gene symbols for
each group.
one of the investigations where nonwhite
sheep showing white markings combined
with dominant black were mated to white
sheep has account been taken of the pos-
sibility of the occurrence of genes for white
markings in the white parents (Roberts,
1926). It is of special interest to note that
all the recessive nonwhite Merinos shown
in photographs by Brooker and Dolling
(1965) show white markings. This indicates
that white Merinos may be homozygous for
white markings.
In some of Vasin’s (1928) experiments,
no account seems to liave been taken of the
fact that some of the sheep used as self-
coloured have had some white markings
other than those under investigation.
As the above shows, some of the con-
clusions of the earlier investigations on the
inheritance of white markings are contra-
dicted by the results of the present study.
The situation can only be clarified by
additional experimentation. As a working
hypothesis it seems justifiable to assume
that all types of white markings are due
to homozygosity for one recessive allele at
one locus, and that the white markings are
only expressed in nonwhite sheep. It seems
also justifiable to assume that the extreme
whitefaced breeds such as the Merino, Dor-
Group Caused by genes at Gene action in heterozygotes Gene symbols
I Several loci Recessive ro - r4
2 One locus Dominant with varying manifestation Q
3 One locus Recessive S
4 One locus Dominant, causing piebaldness SP
5 One locus Dominant Sk
The basis for the assumptions about the
inheritance of the white markings above
is well founded for some of the groups and
less firmly demonstrated for others. In only
set Horn and Rambouillet are homozygous
for white markings as well as homozygous
white. The variation in the amount of
white on the body can be explained by the