An international research team this week unveiled a draft of the first bird genome to be sequenced. It comes from a vintage chicken.
The red junglefowl, native to Southeast Asia, belongs to the same species as the world’s domesticated chicken flocks, explains Richard Wilson of Washington University School of Medicine in St. Louis. The junglefowl, however, represents the ancestral lineage.
Most of the sequence of the billion or so nucleotides in the junglefowl’s 39 chromosomes is now available to researchers in a free database, Wilson says. Still in the works is a paper describing that genome, which has about a third of the DNA of the human genome.
Jerry B. Dodgson of Michigan State University in East Lansing, who collaborated with Wilson on assembling the genome, ranks the chicken as a “premier non-mammalian vertebrate model organism.”
It’s a common experimental animal for embryologists. The first tumor-causing virus identified in any organism was the Rous sarcoma virus in chickens. Immunologists found the first distinctions between T cells and B cells while studying the chicken immune system.
Hans Cheng of the Agricultural Research Service in East Lansing says the new sequence will advance his work on resistance to tumor viruses. Geneticists have had three rough maps of the chicken genome, but those versions haven’t been specific enough to pinpoint individual genes.
Cheng says, “You can get to the right state or city, but you can’t get to the right street address.”
Bin Liu of the Beijing Genomic Institute in China and his team are already using the junglefowl’s new gene sequence to begin searching for agriculturally important variations in the genomes of three types of domestic chicken.
The junglefowl genome should also illuminate some interesting evolutionary issues, says Hans Ellegren of the University of Uppsala in Sweden, who studies sex chromosomes. For instance, in mammals, a tiny Y sex chromosome and a big X yield a male and two Xs make a female, but birds live in a mirror-image world where a big Z chromosome pairs with a tiny W chromosome to yield a female and two Zs make a male. “Is it the presence of the W or the number of Zs that matters?” Ellegren asks.
Also, chicken chromosomes show great size variation. Thirty of the chromosomes are called microchromosomes, being less than one-tenth the size of the chicken’s largest chromosome.
The chicken joins a diverse group of sequenced organisms, including people, dogs, mice, puffer fish, sea squirts, malaria-carrying mosquitoes, rice, and various microbes.