The Equine Genetic Toolbox

Genetic testing reveals differences in an individual’s DNA that result in traits from coat color to muscle function.

Photo: iStock

Kathryn Graves, PhD, associate professor and director of the Animal Genetic Testing and Research Laboratory at the University of Kentucky, spoke about genetic testing at the 6th Annual Kentucky Breeders’ Short Course in Lexington, Kentucky. Genetic testing encompasses any test that detects differences at an individual’s DNA level. This includes parentage, heritable disease, and trait testing.

DNA is made up of four nucleotides, or basic structural units, labeled A, C, G, and T. Microsatellites are DNA segments made of short, repetitive nucleotide sequences (e.g., CACACACA). Researchers can use microsatellites to study parentage, because each one has a number of possible variants (alleles) based on the number of repeats. The Animal Genetic Testing and Research Laboratory uses 17 microsatellites to generate DNA profiles for individual horses as well as to confirm parentage.

Scientists can also use microsatellites to find mutations by comparing the alleles of microsatellites present in affected versus normal horses for a disease mutation or color variation. The closer a marker is to the gene, the greater the linkage (association). The researcher can then use the gene map to look for genes near markers and to sequence the gene.

Another type of marker are single nucleotide polymorphisms (SNPs)--a single base change in the DNA sequence that can have profound effects on phenotype (all of an organism’s observable characteristics). Many SNPs are responsible for coat color variants but can also be associated with other traits such as fertility, body type, muscle function, dwarfism, and more.

During her presentation, Graves spent a substantial amount of time discussing coat color genetics in particular. She broke down the genes and characteristics of various coat colors, as well as the homozygotes (an organism with identical pairs of genes, or alleles, for a specific trait) of mutations. She also discussed cloning and the reasons for its use. She said cloning can be used to recover a valuable breeding animal, create a breeding animal from a gelding or infertile mare, recreate a successful performance animal, or to reproduce an animal because of emotional attachment.

Graves concluded by explaining that genetic testing is still in its early stages. She said that, moving forward, it is important to not try to eliminate genetic disease genes in horses too quickly. There is the danger of eliminating good traits accidently by removing all carriers of an undesirable trait. Tests for complicated traits, such as performance, and complex diseases, such as laminitis or developmental disorders, are on the horizon. However, the current tests available are useful tools to avoid producing horses with heritable diseases, and breeders should use them if one of those diseases is present in their breed. They can use the color gene tests to produce horses with coat colors that make them more marketable or to avoid problems caused by some of the coat color mutations that are deleterious when homozygous. The bottom line is that breeders need to take advantage of the genetic tools available to increase their chances for the best possible outcomes.

Hannah Forte is a communication intern with the UK Ag Equine Programs and Gluck Equine Research Center and undergraduate student majoring in community and leadership development at UK.

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