Íslenskar landbúnaðarrannsóknir - 01.03.1970, Blaðsíða 106

104 ÍSLENZKAR LANDBÚNAÐARRANNSÓKNIR
of F^-progeny from two black Karaknl
rams and white ewes describes 2 darkbrown
lambs by one of the Karakul rams. This
ram sired altogether 94 lambs, 92 black
and 2 brown. Duck describes these lambs
as not being true red, but more of a choco-
late red colour, and more black than red.
One of these lambs was out of a Leicester
ewe and the other out of a Lincoln ewe.
The colour of these two brown lambs
seems to have been the same as or similar
to that found in recessive brown sheep by
Vasin (1928), and therefore possibly also
the same colour as he found among Kara-
kuls in Turkestan near Rokhara. Vasin de-
scribes that colour as black with a golden
sheen and points out that it is similar in
appearance to the recessive brown in north-
ern shorttailed sheep and Merinos.
If one assumes that the dominant in-
tensifier operates independently of whether
the pigment is black or brown, sheep carry-
ing the intensifier and homozygous or
heterozygous for recessive black pigment
would be black, wliile sheep homozygous
for genes for brown pigment would be
brown. The occurrence of the two dark-
brown lambs described by Duck, which
has not yet been explained satisfactorily,
would then have been due to the presence
of the gene for recessive brown in hetero-
zygous state in the Karakul ram, and re-
cessive brown occurring at a very low fre-
quency among the white ewes in the
parental generation. Brown animals among
the Fj’s would then only be expected when
the gene for recessive brown was obtained
from both parents. Some Cheviots were
used in Duck’s experiments, and none of
them gave any brown progeny, when mat-
ed to the Karakul rams. The Cheviots used
in Ewart’s (1919) experiments, on the
other hand, were shown to carry recessive
brown, so brown lambs would have been
expected from them in Duck’s experiments
if all Cheviots carried recessive brown.
Russian experiments (Nikoljskij et. al.,
1929, quoted by Bonikowsky, 1935) involv-
ing so-called coffee-brown or milk-coffee-
brown sheep also support the hypothesis
that recessive brown in homozygous form
would be expressed as brown in presence
of the intensifier.
2. Reddish brown
Duck (1921, 1922) reports a second type
of brown in his crosses, which he calls true
red. This seems to be the colour most com-
monly referred to as dominant brown
Adametz, 1917, Vasin, 1928, Bonikowsky,
1935).
The description of the dominant brown
given by Vasin (1928) indicates strongly
that this colour is comparable to the tan
colour found in the Icelandic sheep, and
that this colour is only expressed in the pre-
sence of the gene for white. Adametz (1917)
showed that the dominant brown sheep in
his study had lightcoloured horns and
hoofs, which siqiports the hypothesis that
they carried the gene for white and were
of a dark tan colour. Crossings carried out
by Bonikowsky (1935) between brown
Karakuls ancl white European breeds and
his backcross of a brown Karakul-Rhön
F^-ram to Rhön ewes also support this
hypothesis. The results reported by Duck
(1921, 1922), where a heterozygous Karakul
ram was mated to black Karakul X white
Fx-ewes, are also consistent with the same
liypothesis.
Henseler (1913) obtained some white
lambs with brown markings and wild type
coloured lambs in an F2 out of a Merino X
Somali-cross, and these lambs have most
likely been tan-coloured.
Nikoljskij et. al. (quoted by Bonikow-
sky, 1935), when mating a seemingly hetero-
zygous black Karakul ram to coffee-brown
fat rump ewes obtained 15 black lambs,
16 coffee-brown, one fox-red and one