The zebra finch is only the second bird to have its genome decoded. The first was the chicken, which also was sequenced at Washington University's Genome Center. The two birds split from a common ancestor about 100 million years ago, and their genomes share many characteristics. Both are tight, compact and roughly one-third the size of the human genome: 1 billion units of DNA in the birds versus 2.8 billion in humans.

Interestingly, both birds lack the nervous system gene neuronal protein synapsin 1, a member of a family of synapsins that have been linked to schizophrenia and seizures. This gene has been found in humans and all other animals whose genomes have been sequenced to date - mammals, amphibians and reptiles, including the crocodile, a "sister" to birds in the evolutionary tree. Comparative studies with other animals suggest that the gene was lost eons ago in an ancestor to modern birds, perhaps in dinosaurs capable of flight.

Unlike the chicken, which clucks but does not communicate by vocal learning, the zebra finch retains a great amount of flexibility in the brain to learn bird song.

A comparison of the zebra finch and chicken genomes also reveals some profound differences and suggests several paths through which evolutionary forces may have combined to produce birds capable of vocal learning.

These include the accelerated evolution of ion channel genes in the zebra finch brain, which are known to play important roles in behavior and neurological function; the way genes on the male sex chromosomes are expressed; and the duplications of genes in the zebra finch that produced new variants of neurobiologically important genes.

"We don't have the complete picture yet," Warren says. "Scientists will need to determine when these characteristics arose during avian evolution and what their significance is. This work would not be possible without having the complete zebra finch genome in hand."

Also on the horizon is the sequencing of the parrot genome, which is slated for completion later this year. That project is a collaboration between Washington University's Genome Center and Duke University.

SOURCE Washington University School of Medicine