An international team of researchers has decoded the genome of the domestic horse Equus caballusAnd have revealed a genomic structure with striking similarities with humans and more than one million genetic differences between different breeds of horses. The work, published this week in ScienceSheds light on a key part of the mammal branch of the evolutionary tree, and provides a starting point to create a map of the genes that cause disease in horses.
“Horses and humans have similar diseases, so that identification of the culprits in horses promises to bring a deeper understanding of the diseases in these two bodies. The horse genome sequence is a key resource enabling us to achieve this goal, “said Kerstin Lindblad-Toh, an author and chief scientist of vertebrate genomic biology at the Broad Institute of MIT and Harvard (USA). Humans and horses have shared an evolutionary history with implications for both species. Like other mammals, the two species share much of the DNA. The horses also suffer from more than 90 inherited diseases that show similarities to those of humans. Twilight’s DNA was the key To generate a genome sequence of high quality, the researchers analyzed the DNA of a thoroughbred mare named Twilight adult. The mare’s DNA decoded using conventional technology capillary DNA sequencing (known as the Sanger sequencing) to reveal a genome that contains around 2,700 million letters or nucleotides, slightly larger than the domestic dog genome and smaller than the genomes the human and cow. “We are especially grateful to our colleagues in the genetics of the horse community who participated in this project,” said Lindblad-Toh, who is also professor of comparative genomics at the University of Uppsala in Sweden. A feature of the horse genome is the small number of rearrangements of chromosomes that have occurred in horses in relation to humans. During the course of evolution, parts of chromosomes can be transferred to other parts of the genome, or remain in their ancestral order, like beads on a necklace. A situation known by the name of “synteny”. More than half of the chromosomes of the horse show synteny, while in the case of humans only occurs on one chromosome and that of dogs, no less than a third. The mystery of equine chromosomes Genome analysis, which is now published in Science, also intrigues researchers. The centromeres, which are more than just a nexus where they join the arms of the X chromosomes, ensuring that cells inherit copies of each chromosome during cell division. “Despite this vital role, relatively little is known about them. Clearly, contain highly repetitive DNA sequences, but what is less clear is what comes first, whether the centromere or their reps, “says the researcher. Lindblad-Toh and colleagues, including Elena Giulotto University of Pavia (Italy), were surprised to discover a region of chromosome 11 containing a horse developing centromere, which is functional, but frozen in a state of youth. The analysis of this nascent centromere revealed that it contained repetitive DNA, suggesting that first appear centromeres and repetitions do next. “I do not know much about the centromeres, have proved especially complicated because of analyzing DNA sequencing. This result helps to address some important questions about how the centromeres evolve, “says Claire Wade, lead author and professor at the University of Sydney (Australia). Resolve night blindness In addition to sequence the genome of a thoroughbred horse, the researchers also studied the DNA of different breeds of horses, including horse American quarter mile, the Andalusian, Arabic, Belgian draft horse, the Hanover, the Hakka, Icelandic horse, the horse Norwegian fjords and the horse trotting or standardbred. The team studied the amount of genetic variation both within each race and between them to create a catalog of more than one million genetic differences in a single letter (called “single nucleotide polymorphisms or SNPs). Through the catalog of SNPs, the researchers could find the candidate mutation in the Leopard Complex or “speckled Appaloosa” by which the layers of the horses are full of striking white areas with or without flecks of color. The horses with this trait often suffer from night blindness, a disorder that also affects humans. The researchers narrowed the list of genetic suspects to 42 SNPs associated mutations including two residents near a candidate gene involved in pigmentation. “This demonstrates the usefulness of the horse in the mapping of genes that cause disease. By making these resources available to the entire scientific community, we expect to see in the coming years a flood of new results, “says Wade. For centuries, horses have been close companions of humans because it makes first domesticated 4,000 to 6,000 years, and used for its strength and as a means of transport. The functions of the horses have been, over time, displaced by other more sports and leisure. ————————– Bibliographic Reference: C. M. Wade et al. “Genome Sequence, Comparative Analysis, and Population Genetics of the Domestic Horse, Science vol 326, November 6, 2009. DOI: 10.1126/science.1178158 Source: SINC
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