Íslenskar landbúnaðarrannsóknir - 01.03.1970, Page 80

78 ÍSLENZKAR LANDBUNAÐARRANNSÓKNIR
TABLE B9
Sex and colour segregation for singles and t.wins
A. All matings (i, j, k, l = 2, 3, 4, 5)
Type of birth Lamb group
Mating wm nm wf nf Total DF X2
AiAi X AjAj S 84 86 170 1 0.234
T 141 147 288 1 0.042
S + T 225 233 458 1 0.140
AiAi X AkAj S 63 49 112 1 1.750
T 116 92 208 1 2.769
S + T 179 141 320 1 4.513*
AtAj x AiAj S 73 19 65 30 187 3 3.189
T 129 30 122 51 332 3 5.574
S + T 202 49 187 81 519 3 8.471*
AiAj x AkAj S 31 35 56 46 168 3 9.095*
T 92 82 89 87 350 3 0.606
S + T 123 117 145 133 518 3 3.483
AjAj x AjAj S 37 34 37 29 137 3 1.248
T 53 60 67 78 258 3 5.287
S + T 90 94 104 107 395 3 1.972
AiAj x AkAi S 183 231 414 1 5.565*
T 344 352 696 1 0.092
S + T 527 583 1110 1 2.825
Total number of progeny 3320
significant heterogeneity in the bottorn
right lrand cell o£ table 40, which indicates
that the twin-single heterogeneity is differ-
ent for the two mating groups B and C.
Mating group B contains genotypes which
are either homozygous or heterozygous for
the alleles Ax and A5. It is therefore more
likely that this rnating group can yield
some information on the effect of indivi-
dual alleles on the variation than the nrore
lieterogeneous genotypes in mating group
C. Mating group B has therefore been
chosen for a closer examination of the
variation found in tabfes 39 and 40.
The most common cause of disturbed
segregation ratios is differential embryonic
mortality. The results obtained earlier on
the effect of the A^-allele on fertility would
sujrport the view that white ewes had a
higher incidence of embryonic mortality
than nonwliite ewes. If this was the only
explanation, one would expect the non-
white ewes to sliow unaffected segregation
and the deviations from expectation should