Íslenskar landbúnaðarrannsóknir - 01.03.1970, Side 11

COLOUR INHERITANCE IN ICELANDIC SHEEP 9
number o£ main colours in the Icelandic
sheep to 17.
The 17 main colours liave been number-
ed from 01—17. In the following, the
English name to be used in this study is
given together with the corresponding
number given to each main colour. Because
many of these colours have never been
given names before, except in Icelandic,
the most widely used Icelandic name of
each colour is also given. At the same tinre
names of these colours from some other
studies are also given, when it is reason-
ably certain that the colours described
there are phenotypically the same as the
colours in the present study.
In connection with the above colour de-
finitions, it should be borne in mind, that
one cannot assume for certain that two co-
lours which are similar phenotypically, but
occurring in two different breeds are ne-
cessarily caused by the same genes, even if
the mode of inheritance seems to be the
same.
The grey in the Gotland sheep is a
typical example. It seems clear frorn Skár-
man’s work (Skárman 1961, 1963 a, 1963 b)
that the grey colour in the Gotland sheep
resembles to a great extent the grey colour
in the Old Norwegian sheep and the grey
in the Icelandic sheep, but in the Swedish
experiments some very dark animals, com-
pletely black at birth and 2 months, were
included in the grey group. These animals
would rnost likely liave been classified as
black both in Iceland and Norway. Such
differences in the definition of the colours
will naturally affect conclusions about
their inheritance.
C. DESCRIPTION OF MAIN
COLOURS
In order to avoid ambiguity, the char-
acteristic features of the main colours
occurring in the present study are describ-
ed below, and the criteria used for deter-
mining the colour in doubtful cases are
also given.
The colour description refers to colours
at birth, except when otherwise stated.
Colour 01 — white (Plate I, 2)
Black and brown pigment are absent
froni all parts of the animal. Some tan pig-
ment may occur in the Icelandic white
sheep, as mentionecl earlier. Thus some
lambs are born completely white, while
others may be born with an even, tan
(rustred) colour all over the body and on
the extremities. The latter animals will re-
tain the tan colour on head and feet as
adults, and many of the primary follicles
will produce tan-pigmented fibres tlrrough-
out the animals’ life.
Complete absence of tan and full tan
pigmentation at birth are the two extremes
of manifestation of tan pigment, and there
is an almost continuous variation in tan
colour between these extremes.
In the present study, white lambs on
some of the farms in the study have been
given scores for tan colour at birth. The
scoring systern used was initiated bv Dr.
H. Pálsson and had been used at the ex-
perimental farm Hestur for several years
when the present study was started. The
scores were as follows.
Score Amount of tan colour
1 No tan colour visible.
2 Tan colour on liead, íeet or tail.
3 Tan colour on head, feet and tail,
and sorne tan colour on bodv, but
body more white than tan.
4 Tan colour on head, feet, tail and
body, and bocly more tan than
white.
5 Tan colour on head, feet and tail,
and body completely tan.