January 27, 2005
Chicken genome still diverse
Today’s domestic chickens have just as much genetic diversity as their wild ancestor, according to genome scientists analyzing the variations on the newly sequenced chicken genome. The study calls into question the notion that years of inbreeding in domestic animals must necessarily lead to less diversity in their genomes. The results were published in the Dec. 9 edition of the journal Nature.
Dr. Gane Ka-Shu Wong, research scientist in the UW Genome Center and associate director of the Beijing Institute of Genomics, led the group known as the International Chicken Polymorphism Map Consortium. They examined the genome of the red jungle fowl, the wild ancestor of today’s domestic chickens, and the genomes of three types of domestic chickens. The domestic breeds included a broiler, which is specialized for meat production, a layer, which produces eggs, and a silkie, which is used in traditional Chinese medicine. The scientists did a side-by-side comparison, known as a genetic variation map, between each of the domesticated chickens and the red jungle fowl.
Genetic variation maps allow scientists to view individual nucleotides on two different genomes. When they find a nucleotide on one genome that is different from the corresponding nucleotide on another genome, that indicates a change in that nucleotide over time. Such changes are called single-nucleotide polymorphisms, or SNPs (pronounced ‘snips’). Higher SNP rates correspond to higher genetic diversities.
When they analyzed the four chicken genomes, the researchers found a rate of about 5 SNPs per 1000 base pairs, compared to 1 SNP per 1000 base pairs in humans. That rate indicates a high level of genetic diversity in the chickens. There was little difference in SNP rates for comparisons between the wild and domestic breeds versus comparisons between the different domestic breeds. That suggests that domesticating the chickens hasn’t led to a decrease in genetic diversity.
Other scientists had theorized that intensive breeding for agricultural purposes would eventually reduce genetic diversity, which would negatively impact the breed’s long-term viability. Although that is possible, it has not happened in practice. The authors speculate that since genetic diversity is the raw material for continuing improvements in animal breeding, it has never been in the farmer’s interest to reduce this diversity.
“This is good news for environmental advocates, because this means we haven’t harmed the chicken genome through domestic breeding,” said Wong.
Future work by others in the consortium will aim at improving chicken breeds and giving scientists a better understanding of genetically complex traits – a central problem in biology, and one which will impact research on many common human disorders, such as obesity and high blood pressure.
