A molecular test for bird gender

The gender of birds, like that of mammals, is determined chromosomally. Whereas in mammals, males are XY and females XX, in birds females are WZ (heterogametic) and males are ZZ (homogametic) [left]. The sex-linked gene CHD is present as a pair of duplicated  loci on the W and Z chromosomes (CHD-W and CHD-Z, respectively) [middle]. CHD-W and CHD-Z have conserved exons (black boxes) but differ in their intron lengths. A WZ female is therefore expected to have introns of two different sizes, whereas a ZZ male will have only one size class. PCR-amplification of the intron region with conserved exon primers  thus creates a molecular test for bird gender.

In the experiment  shown above, DNA was extracted from five birds of unknown sex and amplified with a pair of exon primers.

Lanes 2 & 5 shows the two-band pattern expected for a WZ female bird.

Lane 3, 4, & 6 shows the single-band pattern expected for a ZZ male bird.