I have RNAseq data of 16 species and I want to analyse the phylogenetic relation between them. For this I need to identify the orthologous genes between them to construct phylogenetic tree. Many tools are available for doing this. They require to perform BLAST analysis first. I need to know how to blast my 16 transcriptomes, Do I need to BLAST them against each other or against any other database as is evident from the literature.