Investigation of the relationship between litter size and polymorphisms in some genes (BMP15, GDF9, BMPR-IB, PRL, GHR, NR5A2) in akkaraman and merinos sheep

Sheep are an important livestock species primarily reared for meat production in many countries today. Litter size, a key trait for lamb meat production enterprises, is a polygenic trait, similar to other economically important characteristics. Litter size in sheep is affected by certain major or candidate genes. In this study, polymorphisms in nine loci across six gene regions, which have been reported to increase multiple births, were identified in a total of 120 samples from the Akkaraman (AKR - 60 samples) and Anatolian Merino (AMR - 60 samples) native sheep breeds. These polymorphisms were determined using PCR, AS-PCR, PCR-RFLP, and T-ARMS-PCR methods. Subsequently, the relationship between the identified polymorphisms and litter size was analyzed using chi-square tests and one-way ANOVA. In the completed master's thesis, 3 out of 9 loci studied in AKR and AMR sheep breeds were identified as monomorphic (BMPR1B/FecB, BMP15/FecXBar, and NR5A2/SNP-T1419C), while the remaining six loci were polymorphic. Genetic diversity parameters (Ho, He, and Ne) were generally observed to be high across the six polymorphic loci. Relationship analyses between the genotypes identified in this study and litter size revealed that sheep with the CC genotype at the NR5A2 SNP (T40C) locus in the AMR breed, and those with the AG genotype at the GDF9 G4 locus in the AKR breed, had significantly higher litter sizes (P < 0.05). The results of the study revealed sufficient polymorphism and genetic diversity at various loci of major and candidate genes associated with litter size in AKR and AMR sheep breeds. In particular, the T40C SNP locus of the NR5A2 gene and the G4 locus of the GDF9 gene appear to be promising markers for use in Marker-Assisted Selection (MAS) programs aimed at increasing multiple births in sheep. As many candidate genes as possible (e.g., NR5A2, PRL), and especially major genes (BMPRIB, BMP15, and GDF9) associated with litter size, should be screened in native sheep breeds and correlated with phenotypic data on multiple births. The incorporation of a large number of major and candidate genes into MAS programs is expected to enhance selection success and accelerate genetic improvement, particularly for polygenic traits.