Morphological differentiation of sex chromosomes in three species of ratite birds

Abstract

Chromosome banding studies allowed us to distinguish the sex chromosomes of the emu (<i>Dromaius novaehollandiae</i>), American rhea (<i>Rhea americana</i>), and Darwin’s rhea (<i>Pterocnemia pennata</i>). In each species, we identified the Z chromosome which is very similar to a carinate Z, and the slightly smaller W chromosome. Contrary to the uniformly heterochromatic carinate counterpart, the ratite W chromosome is euchromatic and retains remarkable banding homology to the Z chromosome.