Development and the brain
The zebra finch genome project [3] has revealed that nearly 10,000 genes are expressed in the forebrain of juvenile birds (50 days after hatching; within the critical period for vocal learning) and adult birds, with an overlap of approximately 91% across these age groups. These results indicate that up to 60% of the genes in the genome are expressed in the brain at any one given time. These findings also suggest that a significant fraction of protein-coding genes (9%) are developmentally regulated in the songbird brain, consistent with previous observations obtained with forward genetic approaches.