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 Some genes can lead to serious deviations from the norm, such as decreasing its viability (sub-lethal effect) or even leading to death (lethal effect). The loss of an animal due to an unfavorable genotype can occur either at the early stage of embryogenesis or sometime after its birth.

 Some genes located on the same chromosome can be linked and transferred together to offspring. Their pattern of inheritance differs from that of unlinked genes.

 A mutation is a change in the DNA sequence of a cell or its locus. The extent of mutations can range from a single or few nucleotides to entire chromosomes. Mutations lead to variation and ultimately the formation of alleles. The allele that exists in its original “normal” form in the species is called wild. Other ­alleles of the same gene are the product of mutations involving the wild allele.

With a basic grasp of the vocabulary I’ve introduced in this first chapter, you’ll be able to now appreciate the genetics of horse color as much as you appreciate the myriad colors themselves. In the next chapter we’ll examine over a hundred colors, how they manifest, and the genetic influences at play. Throughout you will find references to the color photographs you can view in the Color Photo Reference sections.