Íslenskar landbúnaðarrannsóknir - 01.03.1970, Page 79

COLOUR INHERITANCE IN ICELANDIC SHEEP 77
TABLE 38
Survival of lambs from known matings at the A-locus
Colour of parents Survival group Total
Sire Dam al) b c
White White 917 12 36 965
White Nonwhite 714 6 19 739
Nonwhite White 357 6 9 372
Nonwhite Nonwhitc 925 15 31 971
Sum 2913 39 95 3047
1) a: survival until shearing time of ewes
b: born dead or died at or very shortly after birth
c: died between birtb and shearing
AiA5 X A5A5 and A5A5 X A^Ag. It has
also been pointed out earlier that matings
involving white parents sliow subnormal
variation, see e.g. table 27.
In order to examine these plienomena
further, the results from all known mat-
ings were grouped according to sex and
type of birth of lamb, and the matings
were grouped according to whether the
parents were white or nonwhite. Because
the AxAg and A5A5 genotypes when com-
bined showed unexpected heterogeneity
the matings involving these genotypes
were examined separately. Table 39 shows
the segregation ratios for this new classi-
fication together with x2’s calculated
among the ratios, while table 40 gives an
overall picture of the x2’s calculated in
table 39.
In table 39 are included only singles of
known colour and sex and twins with
known colour and sex of both lambs with-
in the pair. Lambs from A^A^-ewes were
not included in table 39 and neither were
lambs from A6A5-parents. As a result of
this the numbers in table 39 are lower than
those for corresponding matings in table 9.
The grouping of the segregation results
in table 39 has been used to calculate al-
together 70 x2’s as seen from tables 39 and
40. Of these, 14 show a value which is
significant at the 5 per cent probability
level. This is appreciably in excess of the
number of significant x2’s one would ex-
pect under assumption of random varia-
tion in the segregation ratios in table 39.
It has been pointed out before, in table
28, that tlie proportion of white lambs was
different for the two sexes and also show-
ed a marked difference between singles
and twins. It has on the other hand been
shown in table 27 that the variation in
segregation ratios was abnormally snrall
wlien both sexes and all types of birth were
taken together. In table 27 it was further
shown that this subnormal variation seem-
ed to be connected mainly with matings in-
vofving the A^-allele.
The abnormal variation in the above
segregation ratios is difficult to explain.
The ^2’s in table 40 indicate that there is
a difference between matings B and C with
respect to the underlying cause o£ the varia-
tion. This is particularly shown by the