A PCR-based method for genetic sex identification and evidence of the XX/XY sex determination system in largemouth bass (Micropterus salmoides L.)

Sex dimorphism of economic traits such as growth rate and body size have potential breeding value in aqua-culture. Largemouth bass (Micropterus salmoides L.) is an important freshwater cultured fish in China and the females live longer and reach larger sizes than males. However, the lacking of sex-specific makers and the unclear sex determination mechanism inhibits the development of all-female breeding. In this study, 5 females and 5 males were randomly selected and sequenced with whole-genome re-sequencing technology. In total, 1394 filtered SNPs and 425 filtered InDels were finally identified, and most of these makers were located at Chr7 and Chr18. The validation of the 35 SNPs located at Chr7 in three distinct population (n = 72) indicated that 2 SNPs (S4 and S6) could distinguish the females and males with 100% accuracies, which were genotyped as CC and CG, AA and AT in the females and males, respectively. Further, 10 and 6 InDels with sizes more than 18 bp were finally screened out on Chr7 and Chr18. 2 male-specific InDels (rs3394676 and rs3496814) located at Chr7 could effectively distinguish the above females and males with a PCR-based agarose gel electrophoresis, which per -formed as one band in the females and two bands in the males, respectively. These results suggested the Chr7 might be the sex chromosome and a XX/XY sex determination system in largemouth bass. In conclusion, a whole-genome re-sequencing method was first conducted to provide usefulness sex-specific makers and a XX/XY sex determination system in largemouth bass, which contributes to study of the sex determination mechanisms and the development of mono-sex population breeding.