Historical overview of methods for sex determination in birds

Determining the sex in birds is very difficult, primarily because over 50% of species is monomorphic (no morphological differences between the sexes). Before the application of molecular genetic methods, there were used numerous methods all of which were unreliable. Because of the importance of the analyses, they have to be reliable, economical, safe and prompt. Highly conserved CHD gene is defined in 1995. on W chromosome in birds, while on Z chromosome it was defined two years later. The difference in the length of the intronic sequences of CHD gene of Z and W chromosomes enables the distinguishing of the sexes after amplification of specific fragments by the application of specific primers. Molecular genetic methods have the supremacy over all the other methods because, except for being safe (both for birds and people), they provide reliable results, and also can be applied in all bird species