Estimation of relatedness of thoroughbreds and eight breeds of horses using DNA fingerprinting of whole blood

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Virginia Tech

Horses have been domesticated for thousands of years. Through selection practices horses have been separated into groups that pass on desired traits. We have viewed what the breeders have done at the genotypic level to accomplish their breeds. By using a relatively new technique, DNA fingerprinting, Thoroughbred inbreeding and eight other breeds (Standardbreds, Quarter horses, American Saddlebreds, National Show Horses, Arabians, Morgans, Mustangs and Belgians) have been studied.

The probes CAC5 and YNZ 132 gave the best probability (ranging from 1.9x10⁻¹⁰ to 4.8x10⁻¹⁵) that two unrelated individuals would not have the same DNA fingerprint out of the probes screened.

The level of inbreeding in Thoroughbreds has been estimated by comparing the number of bands shared among these animals to a quasi-natural population (Mustang) and a theoretically known genetic relationship (a sire and his offspring). Using the probes CAC5 and YNZ 132 Thoroughbreds share 20% more bands than the Mustang and 30-50% less than the sire and offspring.

To compare the nine breeds, blood from ten horses from nine different breeds was mixed and DNA fingerprinted. Each lane on the autoradiograph therefore represents one breed. The two probes produced data with a rank correlation of .75 (Kendall's tau) (Ostle,B., 1963). Selection practices have been divided into, narrow selection regimes (where one or two traits have been selected for) and broad selection regimes (where numerous traits have been selected for). The amount of bands shared between the breeds was calculated and applied to a computer program named Gendiv (Gentzbittel and Nicolas, 1989,1991). Three consensus trees were derived showing that the narrow selection regime breeds, Thoroughbreds and Standardbreds, were the most genetically distanced from broad selection regime breeds, Mustangs and Morgans.