Overview

The record for the oldest genome sequence reconstructed by scientists to date has been broken in Canada, where the bone of a horse’s foot, frozen for approximately 560,000 to 780,000 years, has been uncovered and sequenced. This is the oldest genome sequenced by almost an order of magnitude (ten times), according to Eske Willerslev of the University of Copenhagen.

Method and Process

Scientists initially uncovered the horse bone fragments in 2003 from the Arctic permafrost, and found collagen and protein using mass spectroscopy. Mass spectroscopy is a technique that shows the spectra of molecules in a sample in order to deduce the chemical composition of materials present in the sample. The study yielded a 1.12-times coverage draft genome from the horse bone by combining DNA sequencing techniques in order to maximize DNA coverage. The combination of the permafrost preserving the genetic makeup of the DNA and the techniques for processing the DNA sequence, which involves next-generation sequencing with single molecule real time sequencing, prevented the majority of loss of DNA.

Conclusions of the Study

The purpose of the study was to compare the sequence of the Middle Pleistocene horse found in the Arctic permafrost against the genetic sequence of the genome of a Late Pleistocene horse (about 43,000 years ago), as well as the modern genomes of five domestic horse breeds and a donkey. The results of the study are stunning, and indicates that the Equus lineage represented by the genetic sequence reconstructed from the horse bone fragment gave rise to all contemporary horses, zebras and donkeys in 4 to 4.5 million years before present. The study found that horse populations fluctuated with major climatic events over the past 2 million years. The study also found evidence for evolutionary processes in the horses, especially in their immune systems and olfactory systems through natural selection. Furthermore, the study found that Przewalski’s horses (wild horses) had significant genetic diversity and diverged from domestic horse populations between 38,000 and 72,000 years before present. The scientists concluded that the wild horses are worthy of conservation due to their genetic diversity and lack of intermixing with domestic horses after their divergence.

The Future of Genetic Sequencing

While the leap in genetic sequencing is already impressive, researchers are predicting that human efforts to sequence ancient DNA can surpass even the record set by the study. According to Ludovic Orlando, the co-author of the study, DNA studies may be able to go “most likely up to a million years” back in time, given the optimal processes and the necessary environment to preserve the structural integrity of the DNA sequence, such as the cold and dry atmosphere of the Arctic permafrost. The ability to sequence DNA from such a long time ago can greatly enhance the ability of researchers to reconstruct the evolutionary and genetic history of organisms and even help create a detailed picture of human evolutionary history. It can also help scientists discover and infer the common ancestors for previously unrelated species, as the study demonstrated with domesticated horses, wild horses, zebras and donkeys.

About Author: Danny Sarmiento is working as staff in dna diagnostics center. He enjoys answering questions about paternity, genealogy, and any other type of testing done.
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