# Genome-Wide Association Study (GWAS) on Reproductive Seasonality in Indigenous Greek Sheep Breeds: Insights into Genetic Integrity

## TL;DR

This study explores the genetic basis of reproduction seasonality in Greek sheep breeds using GWAS, finding that the MTNR1A gene is the main determinant.

## Contribution

The study provides insights into genetic integrity and seasonality in indigenous Greek sheep breeds through GWAS and population analysis.

## Key findings

- GWAS analysis found no additional genetic loci correlated with reproduction seasonality beyond the MTNR1A gene.
- Principal component and phylogenetic analyses revealed significant genetic differentiation in national stationary stock groups.
- The study highlights the role of Greek national stationary stocks in preserving genetic integrity of indigenous sheep breeds.

## Abstract

A key feature in sheep biology is reproduction seasonality which concerns the cyclical occurrence of natural breeding, which therefore does not take place throughout the year. Since sheep are short-day breeders, the amount of daylight has an impact on their reproductive activity. The melatonin receptor subtype 1A (MTNR1A) gene is the primary gene that has been linked with seasonality. Nonetheless, information regarding the potential genetic association between other loci and the seasonality of sheep reproduction is scarce. Genome-wide association study (GWAS) is considered a cutting-edge methodology for comprehending the genetic architecture of complex traits since it enables the discovery of many markers linked to different features. In the present study, three indigenous Greek sheep breeds were investigated using GWAS—two of which presented strict patterns of reproduction seasonality, i.e., the Florina and Karagkouniko breeds, while the third one, i.e., the Chios breed had the ability to exhibit estrus throughout the year—in an attempt to detect the genetic loci linked with reproduction seasonality. All three breeds of investigated animals were purebred with Chios and Florina breeds originating from the Greek national stationary stock, whereas Karagkouniko originated from a commercial farm. Interestingly, a significant genetic differentiation of the national stationary stock groups was suggested by principal component analysis, phylogenetic analysis, and admixture and spatial point patterns, with these two breeds being less heterogeneous. This finding highlights the value of stationary stocks towards the maintenance of genetic integrity in indigenous sheep, demonstrating the Greek station’s critical role in the conservation of native sheep breeds. On the other hand, according to the GWAS data analysis, no genetic loci were correlated with reproduction seasonality, emphasizing the MTNR1A gene as the main determinant of the seasonality in native non genetically improved breeds.