Comparison of three different primer sets for sexing birds.

Because many bird species are monomorphic or only sexually dimorphic in adult stages, it is difficult to determine their sexes, which may cause significant problems in population and conservation studies. DNA-based sexing relies on the chromodomain helicase DNA binding ( CHD) gene located on the W chromosome and its homolog on the Z chromosome, giving distinct banding patterns on agarose gel as a result of length differences in intronic regions within this gene. We used 3 specific primer sets, CHD1F/CHD1R, 2550F/2718R, and P2/P8, for sex determination of 230 samples from 77 avian species. We report here the records for 70 of those species analyzed using the CHD1F/CHD1R primer set, and 49 species using 2550F/2718R, and 46 species using P2/P8. CHD1F/CHD1R PCR products on agarose gel generally showed an apparent single band in males and 2 bands in females, but the products of 2550F/2718R (61%) and P2/P8 (42%) showed distinct banding patterns for separate bird orders. However, when PCR products of these last 2 primer pairs labeled with fluorescent dye were run in a capillary gel and detected using a DNA analyzer, P2/P8 gave 2 distinguishable peaks in females, whereas 2550F/2718R results remained the same. DNA sexing with any of those 3 primer sets can be used for all sexually monomorphic avian taxa although the primer sets should be compared before choosing the most efficient one for molecular sexing of the studied species.