Íslenskar landbúnaðarrannsóknir - 01.03.1970, Page 27

COLOUR INHERITANCE IN ICELANDIC SHEEP 25
Of the 4 progeny out of white ewes, 3
were white and 1 brown mouflon.
Of the remaining 38 lambs 17 were white
and 21 nonwliite.
As table 3 shows, all the nonwhite pro-
geny of ram No. 01079 showed the mou-
flon pattern. Of these, 8 were out of black
or brown ewes without pattern, and they
showed only the mouflon pattern ancl
neither grey nor badgerface pattern.
Lambs out of grey, greybrown and black
badgerface ewes on the other hand showed
their own pattern in addition to the mou-
flon pattern in 7 lambs, and the mouflon
pattern alone in 4 lambs among their 11
nonwhite lambs. This is consistent with
expectation under the assumption that all
these ewes were heterozygous for their own
pattern. Ram No. 01079 has therefore only
carried the gene for the mouflon pattern
and not for the others.
The results obtainecl from the progeny
of ram No. 01079 indicated strongly that
the genes for white and the mouflon patt-
ern were allelic.
As regards the genes for black ancl brown
pigment it is clear from table 3 that ram
No. 01079 was carrying both of them. In
matings to ewes with brown pigment (grey-
brown and brown) he produced 7 non-
white offspring, of which 3 showed black
pigment and 4 brown pigment. In matings
to ewes with black pigment known to be
carriers of the gene for brown pigment, 3
lambs were produced, 2 with black and 1
with brown pigment.
It became clear from the above that
the genes for black and brown pigment
were not at the same locus as the gene for
the mouflon jiattern.
Had either one of the genes for pigment
been allelic to the mouflon gene, one
would have expected segregation into e.g.
black mouflon on one hand and brown
without pattern on the other hand, or
into brown mouflon versus black without
pattern. As all the nonwhite progeny re-
ceived the mouflon gene from their sire
and either the gene for black or the gene
for brown, the latter two segregated inde-
pendently of the mouflon gene.
This discovery also lecl to the necessity
of postulating a separate gene for no patt-
ern as a recessive allele to the genes for
grey, badgerface and mouflon. As the pig-
ment genes were found to be at a different
locus from the pattern genes, and as all
the pattern genes were found to be epi-
static to the pigment genes, it became
clear that absence of pattern could only
occur when the animals were homozygous
lor a recessive gene without effect on pig-
ment, and allelic to the pattern gene.
4. Hypotliesis about colour inheritance
in the Icelandic sheep.
On the basis of results obtained from
the experiments and investigations describ-
ed so far, a working hypothesis about the
inheritance of colours in the Icelandic
sheep could be formulated. The hypothesis
is shown below where the gene symbols
used in the present study are also given.
Black pigment was assumed to be pro-
duced by a single gene, B4 and brown pig-
ment by its recessive allele, B2.
The four basic patterns, grey, badger-
face, mouflon and grey mouflon were pro-
duced by 4 separate, allelic genes, A2, A3,
A4 and A6, and absence of pattern by a
5th allele, Ag. The gene for white was also
found to belong to this series and was
given the symbol Aj.
Absence of white markings in nonwhite
sheep was assumed to be due to a single,
dominant gene and presence of white
markings by its recessive allele, S2, in
homozygous condition.
The dominance relationship among the
A-alleles appeared to be as follows: