Association of novel polymorphisms of forkhead box L2 and growth differentiation factor-9 genes with egg production traits in local Chinese Dagu hens

Transcription factor forkhead box L2 (FOXL2) and growth differentiation factor-9 (GDF9) genes have critical roles in the regulation of hen ovarian development. In the present study, these genes were explored as possible molecular markers associated with BW, hen-housed egg production, and egg weight in Chinese Dagu hens. Samples were analyzed using the PCR-single strand conformation polymorphism (PCR-SSCP) technique followed by sequencing analysis, and two novel single nucleotide polymorphisms (SNPs) were identified within these candidate genes. Among them, an A/G transition at base position 238 in the coding region of the FOXL2 gene and a G/T transversion at base position 1609 in exon 2 of the GDF9 gene were found to be polymorphic and named SNPs A238G and G1609T, respectively. The SNP A238G (FOXL2) leads to a nonsynonymous substitution (isoleucine77-to-valine), and when the 360 Dagu hen samples were divided into genotypes AA and AB, allele A was found to be present at a higher frequency. Furthermore, the AA genotype correlated with significantly higher hen-housed egg production at 30, 43, 57, and 66 wk of age and with a higher egg weight at 43 wk (P<0.05). For the SNP G1609T (GDF9), the hens were typed into TT and TC genotypes, with the T allele shown to be dominant. The TC genotype was also markedly correlated with higher hen-housed egg production and a higher egg weight (P<0.05). Moreover, four haplotypes were reconstructed based on these two SNPs, with the AATC haplotype found to be correlated with the highest hen-housed egg production at 30 to 66 wk of age and with higher egg weights at 43 wk (P<0.05). Collectively, the two SNPs identified in this study might be used as possible genetic molecular markers to aid in the improvement of egg production traits in chicken breeding.