Dr. Fernando Marques, a professor and veterinarian at the Western College of Veterinary Medicine, explains that knowing how genetics works can provide some answers to those questions about genetic diseases, and allows you to make better decisions about breeding for a healthy foal.

โ€œSome diseases have autosomal recessive modes of inheritance,โ€ he says. โ€œThat means only individuals which are homozygous-recessive โ€“ those who carry two copies of the allele that codes for the recessive trait โ€“ are affected and show clinical signs of the disease. Heterozygous animals that have two different copies of the allele, one dominant and one recessive, are carriers and do not show clinical signs.โ€ In fact, he adds, you canโ€™t distinguish clinically the โ€œcarrierโ€ from the horse who has two of the dominant (healthy) alleles.

Itโ€™s all in the alleles

In simpler language: all of the horseโ€™s traits are coded in his alleles. For each trait, the horse has one allele from his mother, and one from his father. The sperm cells (in the male) and egg cells (in the female) are the only ones that contain just one allele for each trait โ€“ when they are formed in the body, the cells split in half so that each has just half of the animalโ€™s genetic code.

Advertisement