molecular test for bird gender
The gender of
mammals and birds is determined chromosomally. However,
mammals are XY
birds it is
the females that are
heterogametic (WZ) and males are homogametic (ZZ) [below, left]. As
this makes a convenient test for geneder possible. In
species of seabirds, the sexes are not strongly
differentiated morphologically. Characterization of the
sex-chromosome-specific gene locus CHD (chromo - helicase - DNA
binding protein) makes a definitive gender-identification
test possible (Fridolfsoon & Ellegren 1999. J Avian Biol 30,116).
is present as a pair of duplicated gene loci on the W and Z
chromosomes (CHD-W and CHD-Z, respectively)
have conserved exons (black boxes), but differ in their
intron lengths (450 vs
respectively). A WZ female
is therefore expected to have introns of two different sizes,
whereas a ZZ
male will have only one size
In the above
experiment, genomic DNA extracted
five whiskered auklets (Aethia
pygmaea) has been amplified with a pair of conserved
exon PCR primers (2550F and 2718R) (Jones, Fraser, Rowe, Carr, & Taylor.
2002. Auk 109,1064). In the picture ar right, the left-most
is a molecular weight
standard: the fourth band from the top corresponds to 603bp.
shows the two-band pattern
600bp above) characteristic of a WZ female bird. Lane 3, 4,
6 shows the single-band
(600bp only) characteristic of a ZZ male bird.