Effects of crossbreeding and inbreeding on the frequencies of blood groups in three breeds of sheep

Abstract

Blood groups were determined for eight loci in a total of 742 sheep and for the Tf (transferrin) locus of 512 sheep comprising the Scottish Blackface, the Cheviot and the Welsh Mountain breeds and their crosses. Each breed and cross was represented by a noninbred F2 generation and by three stages of inbreeding (25, 37-J-and 50%). The loci for which all genotypes were distinguished were Hb, M, and Tf, and those for which partial description (including the recessive homozygote) was made were A, B, C, D, R and i. There were large differences among the three pure breeds only for the frequencies at the Hb and Tf loci. The homozygote frequencies of the Blackface-Welsh and Cheviot-Welsh crosses were approximately half-way between their respective pure breeds. For the Blackface-Cheviot cross the homozygote frequency was considerably lower than either parental breed, suggesting that over all loci there were greater differences in gene frequencies between these two breeds than between the Blackface and Welsh or Cheviot and Welsh. On average over all loci (except Tf) inbreeding had the effect of decreasing heterozygosity roughly in relation to expectation. Individually this effect was statistically significant only for ii, M h M b , Hb A Hb A and Hb b Hb b . For the Tf locus there was no average decrease in heterozygosity as a result of 25 % inbreeding but thereafter there was a greater decrease in the purebreds than in the crosses. There were small (< 0-20) but significant residual correlations between R-O-H blood types and genotypes at several other loci, and between dd and the M system genotypes.

Genetic Polymorphisms and Their Relationships with Inbreeding and Breed Structure in Rare British Sheep: The Portland, Manx Loghtan, and Hebridean

“…Significance of dif@rences among czasseS of inbmeding chf = 9.77, grounds (Falconer 1960) and observed in practice in Scottish hill sheep (Rasmusen et al 1974) as well as in the present study (Table 8).…”

“…A record can be made of the frequencies of certain alleles, and future workers would then be able to compare these frequencies with contemporary records to check whether genetic conservation had been achieved. Many protein polymorphisms exhibit codominance, i.e., the heterozygous form can be distinguished from the homozygous, and when they are investigated in pedigree populations (Rasmusen et al 1974) they make it possible to observe the reduction in heterozygosity which is the predicted consequence of inbreeding.…”

Lamb survival as affected by inbreeding and cross-breeding

“…They further indicated that this could be related to the environment. On the other hand, Rasmussen et al (1974) observed that in some British sheep breeds and their crosses inbreeding had the effect of decreasing heterozygosity roughly in relation to expectation. Curvilinearity of the effect of inbreeding on economic traits has been reported in other species (Dinkel et al 1968) while Bereskin et al (1968) demonstrated that the equation representing the relationship between 154-day litter traits in pigs and inbreeding of the 1-2 litter was cubic.…”

Transferrin polymorphism in Herdwick sheep

“…(1963) identified the frequency of transferrii types and alleles in a flock of Welsh Mountain Sheep, and Rasmusen et al (1974) typed three breeds of sheep, Welsh Mountain, Cheviot and Scottish Blackface, with respect to transfenin types. Taking the data given by Rasmusen et al (1974), it would appear that the Herdwick Sheep at Compton are somewhat similar to the Scottish Blackface, having T f B and T f D present at the highest frequency, with Tf4 and Tfc present at a very low frequency, and an absence of the TfE allele. Whether conclusions can be drawn as to the origins of the two breeds being common it is not possible to state until other genetic parameters in the blood can be identified.…”

“…However, there is the ,problem of generality within one breed. The data on the transferrin types in the Welsh Mountain Sheep from the two sources (Khattab et al, 1963;Rasmusen et al, 1974) give varying frequencies for the transferrin types but they do have the same trend in the frequencies. The foundation flock of Herdwicks at Compton originated from five individual flock obtained over a wide area, and can therefore be considered to be genetically diverse.…”