This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A mule has helped researchers build the most complete reference genomes to date for horses and donkeys, giving scientists access to complex regions of DNA that earlier versions could not fully capture. Led by researchers at the University of Kentucky Martin-Gatton College of Agriculture, Food and Environment (CAFE) and published in Cell Genomics, the international study introduces new genomes that provide a clearer view of centromeres, telomeres and other highly repetitive parts of chromosomes.
These historically impossible-to-assemble regions are important for understanding how chromosomes work, how species evolve and genetic differences that may affect animal health and physical traits. Ted Kalbfleisch, Ph.D., a researcher in the UK Department of Veterinary Science, led the project. Kai Li, also in the Department of Veterinary Science, was one of the study's lead authors.
"For a long time, some of the most complex regions of the horse genome were essentially invisible to us," Li said. "With this new reference genome, we can finally begin to explore those regions and ask how they contribute to chromosome biology, genetic diversity and traits that matter in horses." The researchers created new horse and donkey genomes using DNA from a female mule. A mule receives one set of chromosomes from its horse mother and another set from its donkey father.
Scientists can distinguish the two sets because the DNA contains enough differences, making the mule an especially useful animal for this project. Instead of trying to separate two very similar sets of horse chromosomes, the researchers could identify which pieces came from the thoroughbred mother and which came from the donkey father. Scientists call this process "phasing," allowing the team to reconstruct a horse genome and a donkey genome from the same animal.
The team combined several advanced DNA-sequencing methods. Some produced highly accurate reads on the order of tens of thousands of bases, while others produced extremely long DNA reads (hundreds of thousands of bases). These new technologies made it possible to assemble the highly repetitive telomeres and centromeres.
The researchers also used information about how different parts of chromosomes physically interact. Together, these methods helped them place millions of DNA letters in the correct order. The resulting assemblies are described as telomere-to-telomere, or T2T, genomes.
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