A novel marker for the platyfish （Xiphophorus maculatus） W chromosome is derived from a Polinton transposon

A consensus sequence, encoding a putative DNA polymerase type B derived from a Polinton transposon, was assembled from the sex determination region of Xiphophorus maculatus. This predicted protein, which is 1,158 aa in length, contains a DNAA_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 het- erogamety）, which represent new markers for this type of sex chromosome in platyfish. This marker with W- and Y-specific copies suggests relationship between 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.