Introduction to This Blog

So you've always wanted to own a palomino. Ever since you saw vintage pictures of Roy Rogers riding Trigger, you've dreamed of that golden horse with the white mane and tail.

Or perhaps your dream color is gray or buckskin. Maybe you just love the loud patterns of Bev Doolittle's paintings, or you are captivated by the white Lipizzaner stallions of the Spanish Riding School in Vienna.

If you're like me, you might have wondered where horse color comes from. My curiosity started when I owned my dream horse: a black and white tobiano mare with blue eyes named Apache. I started wondering what caused her loud spotted pattern and whether or not she'd pass on the color to her foal. Why did she have a black and white foal out of a liver chestnut stallion? How will she continue to produce spots?

So I started studying and learned very quickly that horse colors seem extremely complex. However, I discovered that I can break down the information and understand it just by remembering basic biology from high school.

What? That stuff actually can be used in real life? Yep, it can, and I'll explain it briefly here.

When I was in high school, we had a basic introduction to genetics. We learned that genes dictate certain hereditary traits, such as the color of your eyes or hair or why you pick your nose and you friend sucks his thumb.

In humans, animals and plants, genes have two alleles. One allele is inherited from each parent. The sex cells, the sperm and the egg, carry one allele each, and once the sperm and egg meet, the alleles meet up to create the complete gene. Each allele can dictate how a gene is expressed, or genotype, which is the set of alleles for a specific organism. This dictation creates a trait, or phenotype, which is the observeable traits of an organism (blue eyes, or palomino coat).

Genetic studies concerning hereditary traits was extensively studied by Gregor Johann Mendel. Mendel focused on studying pea plants. Pea plants have two different colors of flowers: purple and white, with no intermediate color (such as lavender). Mendel discovered that when he controlled which colors mated, it was clear that color was being controled on a genetic level. White mated with white always produced white, while purple mated with white sometimes produced purple and sometimes produced white. The kicker was that when he crossed purple and purple, it created purple 75% of the time and white 25% of the time. This means that purple is the dominant color. This also means that it is the dominant allele, which means that whenever it is present, the flower will be purple no matter what.

Mendel also discovered that when two purple alleles were present, the flower was homozygous for purple, meaning it would pass on one purple allele each time. If one purple and one white allele were present, the flower was heterozygous for purple, meaning it might pass on the purple allele or the white allele. The white allele is recessive, which means that when the dominant gene (purple) is not present, the color "recesses" back to the basic color, which is white.

This is a chart that shows how genes work in the pea plant (downloaded from Wikipedia.org). To use the chart, we put the male flower on the top and split his alleles into two columns. The female flower goes on the left and her alleles are split into two rows. The capital letter "B" represents purple--it is capitalized because purple is the dominant color. The lowercase "b" represents white and is lowercase because it's recessive. (To wit, all alleles are represented in writing with a capital or lowercase letter, depending on whether the allele dominant or recessive). When we cross two heterozygous purple flowers, expressed as Bb, then we have the chance of four types of offspring. One will be a homozygous purple flower, two will be heterozygous purple flowers, and one will be a white flower. The phenotype of the flowers will be 75% chance of purple and 25% chance of white.

We can change this chart if we wanted to. Try changing the chart to represent a homozygous flower, BB, with a heterozygous flower, Bb. You will discover that the flower will always appear purple, but you have a 50% chance of it being homozygous purple and a 50% chance of it being heterozygous purple.

Since Mendel's time, geneticists have discovered that we can look for certain markers on the DNA chromosome sequence to learn if a human, animal or plant is homozygous for a trait. This is very valuable in being able to predict life-treatening conditions. For example, a test is available to find out if a horse can pass on HERDA or Lethal White Syndrome. This can help us keep from breeding horses with serious medical issues that could or do kill them. It can also help us to learn if a horse is going to pass on a certain color or not.

That's where this blog comes in. We can turn to genetics to study how horses produce certain colors. I find that it's fun to discover how horse color works. I hope it is interesting and fun for you as well.