Identification of Genomic Regions Related to Litter Size With Divergent Selection between Iranian Indigenous Sheep Breeds and Iceland Sheep Breed using FST Unbiased Statistics

Background: Due to the increasing demand for animal products, reproductive efficiency considered as one of the main objectives of sheep breeding, even in cases where the main emphasis is on milk or wool production.In cases the meat production is the main breeding objective, increasing reproductive efficiency is the most important goal of breeding programs.Although increasing fertility in ewe is possible in different pathways, ovulation rate and liter size are the main goals in breeding programs to achieve high fertility.Then, this study was performed to detection selection signature between Iranian native (as a genetic group with low reproductive performance) and Icelandic (as a genetic group with high reproductive performance) sheep breeds, and identify genes related to fecundity and litter size in sheep.Methods: In this regard, the genomic information of 154 samples including 11 Iranian sheep breeds (Kermani, Baluchi, Afshari, Karakul, Sanjabi, SiahKabud, LoriBakhtiari, Shal, Ghezel, Chios, GrayShiraz) and 54 Iceland sheep breeds, were used.The genomic data related to these genetic groups including Icelandic and Iranian sheep breeds were obtained from the iSheep database and the address https://disk.yandex.ru/d/3N2wEv0-9_NL0w,respectively.Quality control of genomic data and filtering was performed using the PLINK software.The individuals and SNP with more than 5% missing genotypes were excluded.Then, the data were screened based on Minor allele frequency (MAF) less than 1%, and Hardy-Weinberg equilibrium (HWE).From the total available data, including 552,847 SNP markers related to autosomal chromosomes with known locations from 204 animals, finally 527,292 SNP markers from 204 animals, with about 0.999376 genotyping rate, was remained for inter-population genetic differentiation and structure analyses.Then, data filtering was done for seprate genetic groups.In this edition of the data, 527,284 SNP markers related to 174 animals were endured to selection signature analysis.Genetic differentiation index analysis (FST) and principal component analysis (PCA) were performed to determine genetic groups using PLINK 1.9 software.Ubiased FST () estimator statistic were used to explore the signs of selection.In order to better identify the selection signals, numerical values of SNP markers were averaged using the creeping window method up to a maximum length of 100 kb for adjacent SNPs.Only 0.1% of the genome regions with the highest values, were identified and determined as selection signatures.The genes related to selected genomic regions was extracted using the BIOMART online database corresponding areas in the sheep genome assembly (Oar 3.1).The detected genes, related to the selected regions, were surveyed by DAVID 2021 (The Database for Annotation, Visualization and Integrated Discovery) and STRING (Version 12) to identifying biological pathways and probably gene interaction networks.Results: According to the principal component analysis (PCA) results, the group with high reproductive performance (Icelandic sheep) is completely separate from the genetic group with low reproductive performance (Iranian sheep breeds).The complete differentiation between two groups with low and high reproductive performance can be related to the regional separation of these two groups.Kermani and Chios breeds (from the Chios breeding center in Kerman province of Iran) are seprated from other Iranian breeds with the second component.It was confirmed by