An international team of scientists has sequenced over 90% of the genome of the domestic turkey (Meleagris gallopavo). Details of the genome, published in the PLoS [Public Library of Science] Biology journal, shed new light on avian biology and could help turkey producers deliver a better product. The work was partly supported by the EU through the QUANTOMICS ('From sequence to consequence - tools for the exploitation of livestock genomes') project, which is funded to the tune of EUR 6 million under the 'Food, agriculture and fisheries, and biotechnology' Theme of the EU's Seventh Framework Programme (FP7). Bird genomes tend to have a small number of large chromosomes (dubbed 'macrochromosomes') and a large number of smaller 'microchromosomes'. So far the researchers have sequenced 93% of the turkey's genome, uncovering some 16,000 genes in the process; most of this data comes from the bird's 10 macrochromosomes. The team is still working out the best way of sequencing the microchromosomes. 'We have already described thousands of genes previously unknown to avian scientists,' commented the lead author of the paper, Rami Dalloul of Virginia Tech in the US. 'In the short term, the turkey genome sequence will provide scientists with knowledge of specific genes that are important in meat yield and quality, health and disease resistance, fertility and reproduction,' added Dr Dalloul. 'For example, we don't always know the mechanism for how host-pathogen interactions work. The genome sequence will allow us to better understand this process, which will in turn give us a better understanding of disease prevention and treatment.' Ultimately, the findings may lead to the development of tools that will enable producers to breed leaner turkeys with improved flavour and texture. The turkey's genome may also have implications in the medical field. Like humans, turkeys are susceptible to a condition called dilated cardiomyopathy, in which the heart becomes weakened and enlarged, affecting its ability to pump blood around the body effectively. Researchers are also interested in turkeys' unusually high sensitivity to aflatoxins. These naturally occurring carcinogens are produced by fungi and suppress the immune system. The turkey is the third bird to have its genome sequenced, the other two being the domestic chicken and the zebra finch. Comparing the turkey and chicken gene sequences highlights the relative stability of genomes in the galliformes (the order of birds to which both species belong). According to the researchers, around 10% of the turkey genome is under 'selective constraint', whereas in mammals the figure is just 5%. In addition, the chicken and turkey genomes remain close, even though the two species split apart twice as long ago as mice and rats, or humans and gibbons. Meanwhile comparing the bird genomes with those of the egg-laying mammal platypus, reveals that while some functions are common to all egg-laying mammals, others are unique to egg-laying birds. Furthermore, birds lack the genes required for mammalian traits such as tooth formation. Looking to the future, the researchers are interested in investigating how domestication has affected the chicken and turkey genomes; after all, both birds have been subjected to intense selection pressure for similar traits. The work on the turkey genome also represents an important advance in genome sequencing research; for the first time, a eukaryotic genome was sequenced by combining information from two complementary next-generation sequencing technologies. As a result, the turkey genome was sequenced much faster than the chicken genome (which was published in 2004) at a fraction of the cost. 'This genome project is a first where the majority of the production cost was invested in analysis and interpretation rather than generating sequence,' the researchers state.
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