SPACA1 and male infertility: Of the seventy-three genes that our study identifies as reproductive tract-specific in humans and for which a published mouse model shows male infertility phenotype (Additional file 14: Fig. S6) [28, 29, 31], it is worth noting that 21 genes—CNBD2, DEFB110, FAM170A, FBXO47, MEIG1, MEIOB, MEIOC, ODF1, ODF4, REC114, RNF17, SPACA1, SPATA22, SPEM1, SPO11, SYCP1, TERB1, TEX19, TEX38, TNP2, and TOPAZ—do not have any associated paralogs and, thereby, may be considered most suitable for further drug development.