Íslenskar landbúnaðarrannsóknir - 01.03.1970, Blaðsíða 23

COLOUR INHERITANCE IN ICELANDIC SHEEP 21
in F2, or in the backcross to the recessive
parental type, segregation of the original
colours and new combinations of colours
are observed. The second approach has
been to collect data on colours frorn flock
books and to regard the matings as repre-
sentative of either pure breeding of the
true breeding parents or as various types
of crosses among the true breeding types
and their crosses.
In the present study, these approaches
were not used. Instead, the experiments
airned at genotyping as many of the indi-
viduals in the experiments as possible with
respect to as many loci as possible. The
genotyping was on the basis of the ani-
mals’ phenotypes, the phenotypes or geno-
types of their parents or the progeny of
the individuals.
For assessment of allelism, animals known
or assumed to be heterozygous with respect
to the genes to be assessed were rnated to
the recessive phenotype. In this way valu-
able information about the mode of in-
heritance could be obtained frorn few
matings, when the heterozygotes were
chosen with care.
The planned experiments reported in
this study were initiated in 1957, and dur-
ing the first 2 years all the experiments
were carried out at the Experimental Farm,
Hestur.
The first step taken in connection with
the study was a search for the phenotype
or phenotypes which could be assumed to
breed true with respect to colour, i.e. the
colour at the bottom of the dominance/
epistasis scale.
From earlier work on Icelandic sheep
(Zóhóníasson, 1934) ancl from examina-
tion of flock books the preliminary con-
clusion was drawn that black and brown
sheep without pattern when matecl to-
gether produced offspring without pattern,
while offspring without pattern often were
obtained from parents showing one patt-
ern. The patterns could therefore be as-
sumed to be dominant or epistatic to no
pattern. It could also be assumed that
brown colour was recessive or liypostatic
to black colour.
It was also obvious that white sheep
could carry genes for nonwhite colour, as
nonwhite progeny out of white parents
were quite comrnon, some showing colour
pattern and some without pattern.
The working hypothesis was therefore
that white colour was at the top of the
dominance/epistasis scale, the patterns
intermediate and no pattern recessive or
hypostatic to both white colour and patt-
erns. At this early stage no definite hypo-
thesis about inheritance of white markings
in Icelandic sheep was available.
In 1950 all the sheep at the Experiment-
al Farm at Hestur had been slaughtered
as part of an eradication policy. No data
from the flock prior to 1951 have been in-
cluded in the present study. When the
farm was restocked in 1951, some black
ewes were bought in, and in addition 2
black badgerface ancl one black nrouflon
ewe. Up to and including 1956, black,
black badgerface and grey rams were used
to some extent on the farnr, and some of
the white rams gave nonwhite offspring
from both white and nonwhite ewes.
In the following, the identification
numbers of the rams and ewes, where giv
en, consist of a 5-digit number. Tlie first
two digits refer to tlre farnr to which the
animal belonged and the last three digits
give the flock book number within the
farm. Farm No. 1 is the Experimental
Farrn at Hestur.
B. EXPERIMENTS
1. Grey nnd badgerface
In the spring 1957 a grey badgerface ram
lamb was born to a grey ram, No. 01035.
and a white ewe, No. 01104. As this lamb