Íslenskar landbúnaðarrannsóknir - 01.03.1970, Blaðsíða 51

COLOUR INHERITANCE IN ICELANDIC SHEEP 49
markings on farm 5 also seems to be the
result of a mutation of Ax to A5.
In cases 6, 9, 11 and 15 white lambs
have been obtained from matings where
both parents were nonwhite. The lambs in
question could all be the progeny of white
rams used on the farms in the same mat-
ing-seasons. The white lamb in case 11 is
thus almost certainly the progeny of a
polled white sire.
The possibility that some of the anomal-
ous white lambs above are of a different
genetic constitution from ordinary white
slieep cannot fully be ruled out, but con-
vincing experinrental evidence for the ex-
istence of a new type of white colour is
still lacking.
3. Contemporary twins by two
different sires
On 1/1/1961 ewe No. 87 on farm No. 2,
brown, genotype AgAgB^B^S^— was mat-
ed to ram No. 02097, a black mouflon,
genotype A^A^B^B^S^—. Later in the
same heat she was accidentallv served bv
a white ram, No. 02088, genotype AtAg
------S2, and the second mating was re-
corded.
The ewe gave birth to twins on 24/5/
1961, one of them black mouflon and the
other white. Frorn the colours of the lambs
they were obviously sired by one sire each.
This indicent demonstrates how easily
accidents of this type may happen and that
although one twin of a pair shows a colour
which determines its sire witliout doubt,
the other twin may be the progeny of an-
other sire.
Cases of unexpected colours out of mat-
ings where the genotype of both parents
is known should therefore always be treat-
ed with suspicion if the observed colour
could have been produced by any other
sire present on the farm during the mating
season.
4. Unexpected colours produced
by a lightgrey ram
In autumn 1962 a lightgrey ram No.
06043, was bought in to farm No. 6 in the
hope that he would be homozygous grey.
The parents of the ram were not known
witli certainty, but were thougt to be a
white sire, genotype A4A4, and a white
dam, genotype Ax A5. He was mated to
ewes with a variety of colours the next
winter, but mainly to nonwhite ewes in
order to produce grey lambs.
In spring 1963 it became clear that the
ram did not give grey colour to any of his
progeny, but out of matings to black or
brown ewes, white, black mouflon and
black lambs appeared.
The owner of the ram was naturally dis-
appointed and wanted to dispose of the
ram, but due to fortunate circumstances it
proved possible to make arrangements with
another farmer who was willing to test the
ram further during the next season by mat-
ing him to nonwhite ewes. The farmer was
paid a fee from the University Research
Institute for each lamb produced by the
ram in this test. The data from this ex-
periment are not included in table 9.
The genotype for the ewes to which the
ram was mated in both years taken together
and the colours of the lambs obtained are
given in table 11.
As seen from table 11, no grey progeny
were produced in matings to A5A5-ewes,
the only colours occurring there being
white, black mouflon and black.
The colour of the ram and the colours
occurring among his progeny indicated
that the ram was of mosaic grey colour,
and that his gonads contained a mixture
of Ax-, A4- and A5-alleles.
If this assumption is correct, one can
divide the lambs into 4 groups according
to the genotype of the dams. The first
group contains white ewes of unknown