Research School of Biological Sciences, Australian National University, Canberra, ACT 2601, Australia. jenny.graves@anu.edu.au
Mechanisms to compensate for dosage differences of genes on sex chromosomes are widespread in animals and have been thought to be critical for viability. However, in birds, compensation is inefficient, implying that for many genes dosage compensation is not critical, and for some genes, dosage differences have even been selected for.