What’s In Your Horse’s DNA?

Geneticists have created tools and tests that help horse breeders select for healthy foals. Furthermore, access to the equine genome means scientists can examine common diseases and conditions and find ways to prevent (and one day treat) them.
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In recent years, laboratory geneticists have created tools and tests that enhance the possibility of producing healthy foals. | Photo: Anne M. Eberhardt/The Horse

Breeders have always been barnyard geneticists, taking a critical look at their broodmares and stallions to create foals with the traits they want, such as color, conformation, speed, athleticism, personality, intelligence, and health.

In recent years, laboratory geneticists have created tools and tests that enhance the possibility of producing healthy foals. Furthermore, the equine genome–the complete sequence of DNA bases, the genes (pieces of DNA that encode molecules such as proteins and determine hereditary traits), and chromosomes (large segments of DNA in each cell’s nucleus)–has been determined. The total amount of DNA and number of genes is broadly similar between horses and other mammals. However, how the DNA is divided into chromosomes varies, explains Ernie Bailey, PhD, geneticist and professor of veterinary science at the University of Kentucky’s Gluck Equine Research Center in Lexington. Each horse cell has 32 pairs of chromosomes–more than human cells, which have 23 pairs each.

All foals inherit their genes from the sire and dam, who each provide one copy of a gene to create a pair. If the two genes are the same type (they have the same DNA sequence or have the same effect), the foal is homozygous for that gene. If the two genes are different, the foal is heterozygous for that gene, Bailey says.

Dominant genes are always expressed when present, and there is a 50-50 chance the parent will pass that dominant gene on to its offspring. An example of a dominant gene is that of gray coat color: Gray offspring always have at least one gray parent. “Only one copy of a dominant gene need be inherited for the offspring to express that trait,” says Bailey

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