Genotype- this is the genetic constitution of an individual, which is determined by the complete set of hereditary factors contained in the chromosomes. This formula contains all possible hereditary factors in his make up, many of which may not be evidenced in the external appearance, which is known as phenotype.

Glass-Eyed- a term used to refer to eyes that are lacking in normal dark pigments in their iris. They can be a variety of colors, but the most often seen is blue. Horses with glass eyes can see just as well as horses with dark eyes. Glass eyes are most common in overo hair coats, but they can also occur in tobianos and solid-colored horses.

Glycolysis- this is the breaking down of sugars into simpler compounds that is performed with or without oxygen in order to produce energy.

Gray- this is a hair coat type of any of the five colors that has a dominant G (graying gene) present in one of the alleles, which progressively whitens the original color until the majority of the hair coat color is white. It can occur in a homozygous or heterozygous condition, which is indistinguishable from appearance. By definition, all gray horses should have at least one gray parent.

Grazer Form- this is a body type that is best adapted for animals that depend on grazing low-lying grasses for their nutrition. It includes extended muzzles, lateral position of the eyes, long appendages, a more horizontal top line with withers and hips that are more or less the same height. These attributes help the animal eat with his head down in open terrain and still be very aware of surrounding dangers when they arise, as well as facilitate rapid flight due to a body form that specializes in forward motion.

Grulla- this is a hair coat color that has the genetic make up of a black or dark bay horse that has received the “D” dilution gene, making the outward appearance of the hair coat color a mousey brown-gray color with black points. In the grulla the dark points not only include the mane, tail and extremities of the legs, but often also include a large portion of the head. Dorsal lines, shoulder stripes and zebra stripes on the forearms are also common.