A New Sex Chromosome Marker, Similar to DNA Polymerase Type B, in the Platyfish Xiphophorus Maculatus

A consensus sequence, encoding a putative DNA polymerase type B, was assembled from the sex determination region of Xiphophorus maculatus. This predicted protein, which is 1158aa in length, contains a DNA_pol_B_2 domain and a DTDS motif. The DNA polymerase type B gene has about 10 copies in the haploid X. maculatus, genome with one Y-specific copy. Interestingly, it has specific copies on the W chromosome in the X maculatus Usumacinta strain (sex determination with female heterogamety), which represent new markers for this type of sex chromosome in platyfish. This marker with W- and Y- specific copies suggests relationship between the different types of gonosomes and allows comparing male and female heterogameties in the platyfish. Further molecular analysis of the DNA polymerase type B gene in X maculatus will shed new light on the evolution of sex chromosomes in platyfish.