Emu are one of the largest living species of birds:
They lay large, blue eggs and have little stripped babies:
|Without arms, emu hug with their minds, or I like to think that they do.|
Like mammals, sex is determined in birds using sex chromosomes, but in birds it is a little different. In mammals (dogs, humans, cows) females have two copies of the same sex chromosome (XX), and males have one X, and one Y, where genes on the Y chromosome turn on the pathways for male features. In birds, it is the males who have two copies of the same sex chromosome (here we call them ZZ), and females who have one Z chromosome and one W chromosome. In birds, male-specific features require expression (product) from two copies of a gene (so males have two Z chromosomes).
|W and Y are usually much smaller than their partners|
But, when Vicoso, Kaiser and Bachtrog looked at the emu sex chromosomes, they saw something really amazing. Whereas the W in most birds is small and degraded (like the human Y), the W in emu is quite large, nearly the same size as it's partner.
|Emu W has nothing to prove to you.|
Proc Natl Acad Sci U S A. 2013 Apr 1.
Sex-biased gene expression at homomorphic sex chromosomes in emus and its implication for sex chromosome evolution.
Department of Integrative Biology, University of California, Berkeley, CA 94720.