Proceedings of the World Congress on Genetics Applied to Livestock Production, 11.826 Genetic parameters and genome wide association study (GWAS) for maternal related traits in Santa Inês sheep breed M.P Berton 1 , S.T. Amorim 2 , S. Kluska 1 , M.V.A. Lemos 1 , B. Olivieri 1 , R. Tonusi 1 , E. Peripoli 1 , J.P. Eler 3 , F. Baldi 1 & J. B. Ferraz 3 1 Faculdade de Ciências Agrárias e Veterinárias, UNESP,14884-900, Jaboticabal, Brazil 2 Universidade Federal de Santa Catarina, UFSC, 88034-001, Florianópolis, Brazil 3 Universidade de São Paulo, FZEA, 13635-900 Pirassununga, Brazil. - Corresponding author: jbferraz@usp.br Summary The aim of this study was to estimate variance components and to identify genomic regions associated with reproductive traits in animals adapted to the tropical climate. The phenotypes information of 1,333 Santa Ines females belonging to four farms located in the Minas Gerais (MG) and São Paulo (SP) southeast states and Sergipe (SE) northeast state of Brazil. The traits maternal efficiency (ME), maternal metabolic efficiency (MME) and twin calving (TC) were studied. The relationship matrix was composed of 32,392 animals, been 576 with genotype information measured using a 12,785 SNPs of the Ovine SNP12k BeadChip (Illumina, Inc.). The variance components and genetic parameters were estimated using a single-trait animal model in BLUP single-step genomic analysis (ssGBLUP). The GWAS analyses were performed using the single-step GWAS methodology by the BLUPF90 family software. The chromosome regions that explained more than 1.0% of additive genetic variance were selected to explore and determine possible quantitative trait loci (QTL). A total of 9, 13 and 11 windows for ME, MME e TC traits were identified, respectively. After gene search, genes related to important functions in uterus (MSX1), embryonic development (OTOP1), reproductive behavior (DRD5) were found. Also, genes with common functions, such as female pregnancy, oocyte development and embryonic development (BCL2, AQP4, ADCYAP1, SMAD4) were also found. Future genomic studies of these characteristics will provide a better understanding of its genetic architectures, since they are of economic importance for the production system. All traits showed low genetic variability and the identified genomic regions hold genes with functions that can influence them, demonstrating the importance of larger genomic studies for sheep breeds, especially hair breeds adapted to tropical conditions that can improve the genetic gain for livestock production by increasing productivity and also reducing the production cycle. Keywords: GWAS, maternal efficiency, Santa Inês breed, Twin birth. Introduction Sheep farming is present in worldwide, and its diffusion is related to the