STUDIES ON GENETIC VARIABILITY IN NELLORE BROWN SHEEP USING MICROSATELLITE MARKERS

Nellore sheep is the tallest mutton breed of India and its home tract is Nellore and Prakasam districts of Andhra Pradesh, but widely distributed throughout the state of Andhra Pradesh and parts of Telangana. Three varieties are distinguished phenotypically based on coat colour as Palla (completely white), Jodipi (white with black patches) and Dora/Brown (completely brown). Nellore Brown sheep are predominantly present in Rayalseema region (Kadapa, Kurnool, Anantapur districts) of Andhra Pradesh. This breed is well known for its disease resistance and thrives well in harsh climatic conditions of Rayalseema. The assessment of genetic variability is important to monitor the gene flow in populations, for conservation of breed and also to determine the level of inbreeding in the population. The present study was undertaken to evaluate the genetic variability present in Nellore Brown sheep population by using twenty four microsatellite markers from the panel of markers recommended by ISAG-FAO for the genetic diversity studies in sheep. A total of fifty blood samples were collected at random from unrelated Nellore Brown animals maintained by farmers in its breeding tract. Phenol-chloroform method was used for isolation of DNA from blood samples. The quality and quantity of isolated DNA was checked using gel electrophoresis and Nanodrop spectrophotometer, respectively. The PCR products were resolved using agarose gel electrophoresis. The allele size for each locus was scored manually from the electrophoresed gels. The allele frequencies, observed number of alleles (Na), effective number of alleles (Ne), observed (Ho) and expected (He) heterozygosity, within population inbreeding estimates (FIS) were computed using POPGENE version 1.32 software. A total of 216 alleles were identified across all the twenty four microsatellite loci studied. The number of alleles at each locus varied from a minimum of four (HUJ616) to a maximum of thirteen (OarCP49) with a mean of 9.0 alleles across all loci. Allele size ranged from a minimum of 75 bp (OarCP49) to a maximum of 297 bp (HSC), while allele frequencies ranged from 0.0102 to 0.3980. The most frequent allele number was nine. The number of effective alleles ranged from 3.8757 (HUJ616) to 9.6232 (OarCP49). The mean number of effective alleles with an overall mean of 6.78 ± 1.79 alleles. The observed heterozygosity ranged from 0.0408 (BM1314) to 0.1429 (OarHH35, OarHH41) with a mean value of 0.0985 ± 0.025, whereas, the expected heterozygosity ranged from 0.7420 (HUJ616) to 0.8961(OarCP49) with a mean value of 0.8409 ± 0.046. All the twenty four microsatellite loci (100 percent) were found to be highly polymorphic and the PIC values ranged from 0.6945 (HUJ616) to 0.8961 (OarCP49) with a mean PIC value of 0.8240 ± 0.061. The inbreeding estimates obtained in this study were all positive and varied from 0.8318 (OarHH35) to 0.9534 (BM1314). The mean FIS value of 0.8825 ± 0.03 indicated the deficiency of heterozygotes. The Chi-square test revealed that all the twenty four loci were showing significant deviation from Hardy-Weinberg Equilibrium.