A new chicken molecular sexing assay based on the Z chromosome dose and the MHM region

Birds have a ZZ and ZW sex chromosome system (male and female, respectively). On the short arm of the Z chromosome of Gallus gallus domesticus there is a repetitive region called MHM region, which is absent on the W chromosome, that causes a natural copy number difference of the MHM region between the sexes, making possible the development of a quantitative PCR (qPCR) sexing assay, based on the Z chromosome double dose. Twenty-seven samples of tissues from eight adult Gallus gallus domesticus (four males and four females) were used to establish the parameters of the MHM copy-number sexing assay. We blinded sexed 20 chicks using 140 samples from different tissues (heart, brain, gonad, kidney, lung, muscle, and blood). The success rate of the assay was 100% (140/140). It required small amounts of DNA (0.39 ng), opening the perspective to the use of the assay in studies in which the amount of available DNA is limited.