Characterisation of the genetic diversity of indigenous sheep populations in Kenya using blood biochemical polymorphisms
Mwacharo, J M
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Six indigenous sheep populations in Kenya generally classified as fat-tailed and fat-rurnped hair types and one exotic breed (Merino) were analysed for variation at five protein coding loci to determine the magnitude of genetic differentiation and relationships among them. A total of 457 animals from farmers' flocks in Kwale, Makueni, Siaya, Kakamega and Kajiado districts, for the fat-tailed and Isiolo district for the fat-rurnped sheep were sampled. Forty animals of the fine wooled Merino breed were used as the reference breed. Two genetically unrelated animals were bled per flock and the blood typed for biochemical polymorphisms at the Albumin, Haemoglobin, Transferrin, Esterase-A and Esterase-C loci, using polyacrylamide gels for Transferrin and starch gel electrophoresis for Albumin, Haemoglobin, Esterase-A and Esterase-C. The loci studied showed variability in the seven breeds with a total of 13 different alleles being observed across the five loci. Albumin exhibited two alleles Albumin-S and Albumin-F. Albumin-S was fixed in Kwale, Makueni, Siaya, Kakamega and Kajiado populations. However both alleles were observed in the Isiolo and Merino populations segregating at variable frequencies. Two alleles were also observed at the Haemoglobin locus: Haemoglobin-A and Haemoglobin-B. Kwale, Makueni, Siaya and Isiolo were monomorphic for Haemoglobin-B, but both alleles occurred at variable frequencies in Kakamega, Kajiado and Merino populations. Transferrin was the most polymorphic locus, with all the five most common alleles (TfA, TjB, TfC, TfD and TjE) observed in the Merino, but only four (TfA, TjB, TfC and TfD) were observed in the indigenous sheep populations in Kenya. TfE occurred exclusively in the Merino but not in any of the indigenous sheep populations studied. Both Esterase-A and Esterase-C exhibited two alleles each in all the breeds studied: the positive and negative variants. Abumin-S, Haemoglobin-B, Transferrin-D, Esterase-A(-ve) and Esterase-C(-ve) predominated over other alleles in all the populations studied. Within breed genetic diversity based on the mean number of alleles per locus, percentage of polymorphic loci and average heterozygosities was low in all the populations studied. The Kajiado population, which showed the highest expected heterozygosity, and allelic diversity, was amongst the populations that recorded the highest percentage of polymorphic loci. Kwale, Makueni and Kakamega populations did not conform to the Hardy-Weinberg equilibrium with respect to Transferrin locus. The FIs, FITand FSTmean values, as measures of population differentiation across all loci were 0.318, 0.374 and 0.083 respectively. Pair-wise genetic distances were estimated between population pairs using four genetic distance measures: Nei's standard genetic distance (Ds), Nei's minimum genetic distance (Dm), Cavalli- Sforza and Edwards chord (De) and arc (Da) distances. Within the indigenous sheep populations in Kenya, the shortest distances were recorded between Kwale and Makueni while the longest distances were observed between Kajiado and Siaya based on all the four distance measures. However, the various indigenous sheep populations in Kenya showed close genetic relationships. On average, Kajiado was the most genetically distant population, recording the highest distances between itself and the rest of the indigenous sheep populations studied. Generally, the overall distance between the Merino and the indigenous sheep populations was as expected, high using all the distance matrices. Phylogenies derived from pair-wise genetic distance estimates, show a clear separation between the indigenous sheep populations studied and the exotic Merino. However, the topology of the former showed rather poor consistency with their morphological classification based on the localisation of fat deposits namely; fat-tailed and fat-rumped hair sheep; suggesting either breed admixture or that the loci analysed do not have a lot to do with the physical regions of fat deposits. The phylogenetic relationship between the indigenous sheep populations revealed two distinct clusters. The first cluster grouped together Kwale, Makueni, Siaya and Isiolo populations. Within this cluster, Kwale and Makueni were grouped together and showed very close genetic relationship followed by Siaya and Isiolo respectively. Kajiado and Kakamega populations were grouped separately in the second cluster. Average genetic distances within and between the fattailed and fat-rumped hair sheep as compared with previous studies of other indigenous livestock breeds, showed that the genetic differentiation of each of the indigenous sheep populations in Kenya is of the same order of magnitude as that among well-recognised and established indigenous breeds of sheep from other countries.