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variability determination in a long-term selected Rhode Island Red chicken strain using microsatellite markers. Vet. arhiv 87, 511-522, 2017. ABSTRACTGenetic improvement needs the existence and precise estimation of genetic variability, and microsatellites are a molecular marker of choice for its assessment. Rhode Island Red (RIR) is a brown-egger chicken breed. A RIR population, selected on the basis of 40-week part-period egg production for 30 generations, maintained as a closed flock to develop multi-colored strains for backyard farming, were studied to determine genetic variability and heterozygosity using microsatellite markers. Genomic DNA from 76 randomly selected birds was analyzed at 10 microsatellite loci, alleles were separated on 3.4% MetaPhor Agarose, sized using Quantity-One software and analyzed by POPGENE v1.32. Nine loci demonstrated polymorphism resolving 30 alleles, the average number of alleles/ locus being 3.00 ± 1.41. Allele numbers varied from two to six and size ranged from 102 to 320bp. The average polymorphic information content and Nei's heterozygosity were 0.3134 ± 0.064 and 0.4119 ± 0.2575, respectively, suggesting these loci to be moderately polymorphic and informative. The observed (N a ) and effective number (N e ) of alleles and Shannon's index averaged 3.0000 ± 1.4142, 2.0324 ± 0.9416 and 0.7342 ± 0.4649, respectively. N e was less than N a at most loci, indicating the prevalence of heterozygosity at these loci. Mean expected heterozygosity was higher than mean observed heterozygosity at most loci, indicating that the population was not in Hardy-Weinberg equilibrium but was under the influence of some forces such as selection, etc. The same was also demonstrated by Chi-square and G-square tests. It may be inferred that long-term selection for 40-week part-period egg production has resulted in Hardy-Weinberg disequilibrium at the studied microsatellite loci, thereby suggesting a probable association between these microsatellite loci and layer economic traits in RIR chicken, and this might be useful in marker assisted selection for egg production in future.

In present investigation, 325 single-hatched RIR chicks that has undergone 30 generation of selection based on 40-week part-period egg production were evaluated for growth and layer economic traits using least-squares analysis of variance. Overall least-square means of body weight at 16, 20, 40 and 64 weeks of age were 1362.6±21.4g, 1791.6±24.5g, 2184.6±26.2g and 2433.8±34.2g, respectively. Males were significantly heavier than females (P£0.001) at all ages. Least-square means of age at sexual maturity, egg weight at 28, 40 and 64 weeks of age, egg number up to 40 and 64 weeks of age were 134.5±0.9days, 44.8±0.3g, 47.73±0.4g, 51.5±0.7g, 118.3±1.2eggs and 214.5±4.8eggs, respectively. Heritability estimates were high for growth and low to medium for layer economic traits. Genetic and phenotypic correlations among body weights were high and positive. The egg production up to 40 weeks revealed high and positive genetic (0.89±0.15) as well as phenotypic (0.63) correlations with egg production up to 64 weeks suggesting the its usefulness as selection criterion for genetic improvement of annual egg production.

Genetic heterogeneity was investigated using 24 microsatellite markers and genomic DNA of 24 randomly selected birds from the selected and control lines of RIR chicken maintained at ICAR-Central Avian Research Institute, Izatnagar. The microsatellite alleles were determined on urea-PAGE, recorded using GelDoc system and the samples were genotyped. The complete genotypic data set was analyzed using POPGENE software. The observed heterozygosity (Ho) means were 0.6306±0.3901 and 0.6528±0.4345 in the selected and control line, respectively. Explicitly the control line contained more Ho mean and thus the more diverse than the selected population. The expected heterozygosity (He) ranged from 0.5053 (MCW0059) to 0.8421 (MCW0004) with mean of 0.7066±0.020 in the selected line, and from 0.2899 (MCW0059) to 0.9130 (ADL0136) with mean of 0.7095±0.030 in the control line. The Ho mean was less than the He mean in each population; the Chi square and G-square tests revealed significant deviations of almost all the loci from the Hardy-Weinberg equilibrium. The selected and control line populations had the corresponding genetic identity and genetic distance of 0.5264 and 0.6418 as original measures, and 0.5528 and 0.5928 as unbiased measures. The phylogenetic analysis revealed their moderate genetic diversity reflecting 29.64 to 32.09% common inheritance. This present investigation thus estimated genetic heterogeneity using a set of microsatellite markers after long term selection for egg production in RIR chicken and could be useful in the study of population dynamics under selection pressure.

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