Primer on genetics and heritability

Since horse domestication occurred, 5000 years ago, people have selected breeding stock from among the most successful horses to produce the diversity of horse breeds we have today. Those who understand the basic principles of genetics are likely to be more successful.

Phenotype = Genotype + Environment (P=G+E)

Phenotype is what we see. We select horses based on their phenotype. Phenotype can include colour, racing performance, gait, appearance and even health. The performance of a racehorse is a product of its maintenance and training (Environment) as well as its inherited predisposition for characteristics of heart, respiration, muscle, endurance and stride length (Genotype). As our management becomes optimised and standard for horses, the differences among horses are more likely to be based on genetics than on management.

Genetics

Genes are the fundamental elements of heredity. Mendel performed famous studies of peas in the 1800s and described them as discrete factors affecting discrete traits. In 1911, Thomas Hunt Morgan demonstrated that genes reside on chromosomes and suggested the mechanism for their inheritance. In 1951, Watson and Crick described the structure of the DNA molecule and how it carried out the functions of heredity ascribed by Mendel and Morgan. The main activity identified for DNA was encoding genes for proteins, known as the Central Dogma. A mechanistic view of heredity was born in which we anticipated that if we could identify the DNA sequence for a trait, we would have a profound understanding of that trait.
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