Polymorphism in a sex‐linked DNA marker located on LG23 in Hainan strain of Nile tilapia (Oreochromis niloticus)

Abstract

AbstractMarker‐5, which is linked to the major sex‐determination gene amhy on LG23, has been used for sex genotyping of various strains of Nile tilapia. Marker‐5 specifically amplifies fragments of approximately 1,422 and 982 bp of the X and Y chromosomes, respectively. Herein, we evaluated Marker‐5 polymorphism in Nile tilapia of Hainan strain, China. Agarose gel electrophoresis showed that in 13 out of 85 female fish, Marker‐5 amplified a larger band, distinct from the standard X‐specific band. Sanger sequencing showed that this larger band was 1,688 bp in length and showed high similarity with both 1,422‐bp X‐specific and 982‐bp Y‐specific fragments. The larger band was proved to be a female sex‐linked allele of Marker‐5 and was labeled as XL. When the polymerase chain reaction (PCR) products of XLY fish, amplified by Marker‐5, were tested by agarose gel electrophoresis, an unusual band, smaller than XL but larger than that of Y fragment, was observed. The unusual band could be a heteroduplex of the XL and Y fragments. In very few XXL male, amhy was found to be linked with 1,422‐bp fragment amplified by Marker‐5. Understanding the Marker‐5 is useful for its utilization in sex‐controlled breeding in farmed Nile tilapia.