Candidate Genes Applications in Genetic Improvement Programs in Chickens

Abstract

The experimental chicken populations (F 0 , F 1 , F 2 and F 3 ) have been constructed all-over the world to be used in gene and quantitative trait loci (QTL) mapping studies in different breeds. The genome-wide QTL are located on seven macro-chromosomes (chromosome 1, 2, 3, 4, 6, 8 and Z) and on one microchromosome (chromosome 11) for body weights and gains, on chromosomes 1 and 5 for egg weight, on chromosomes 5 and 7 for number of eggs and on chromosome 1 for age at first egg. The total chromosomal map length for body weight is 1901 cM ranging from 25 cM on chromosome 11 to 568 cM on chromosome 1, while the total chromosomal map length for egg production and egg quality traits was 1949 cM ranging from 52 cM on chromosome 11 to 542 cM on chromosome 1. The majority of molecular markers used nowadays in poultry are microsatellite markers, STRs (short tandem repeats) and SNPs (single nucleated polymorphism). The microsatellites are used as the most widely markers for the analysis of genetic diversity and population structure in poultry. To detect the genetic diversity in poultry, definite number of microsatellite markers covering nine autosomal linkage groups and the sex Z chromosome are considered in genotyping of F 0 grandparents and F 1 and F 2 offspring. Detailed information about selected microsatellites are available at the FAO website (www.dad.fao.org/en/refer/library/guidelin/marker.pdf). Primarily, the chickens' breeds must be characterized on molecular bases in terms of allelic and genotypic frequencies, the effective number of alleles (Ne), the observed (Ho) and expected (He) heterozygosity, Hardy-Weinberg equilibrium (HWE), the polymorphism information content (PIC) and the F-statistics of the reduction in heterozygosity due to inbreeding within each population (F IS ). The candidate genes located on 18 chromosomes (number