Recombination nodules and axial equalization in the ZW pairs of the Peking duck and the guinea fowl.

The meiotic Z and W chromosomes of the Guinea fowl (Numida meleagris) and the Peking duck (Anas platyrhynchos) show features similar to those described previously for 3 species of Phasianidae: chicken, Japanese quail and bobwhite quail. Axial equalization in the gonosomes of the Peking duck involves lengthening of the W axis along with shortening of the Z axis. A single recombination nodule is constantly found in the synaptic, terminal region of the ZW pairs stained with phosphotungstic acid. The localization of this nodule is significantly different in these two species, but the length of synaptonemal complex harboring the nodules is not significantly different. Based on the phylogenetic distance between the observed species, the present data support the hypothesis that the presence of a pseudoautosomal region is a general property of ZW pairs in carinate birds.