The Basic Colors of Horses

This post has been revised with new photographs here.

I got a new book this week: Equine Color Genetics third edition, by Philllip Spoenenberg. I have the first two editions–and how things have changed since the first edition came out! Even the second edition had only four types of dilution genes. Now there are six, with at least one more that has not been located yet.

Lineback duns and creams were clearly separate by the second edition, which also greatly expanded on silver dapple and added champagne. But the third edition added pearl, mushroom and a rare dilution, probably recessive, found in Arabians.

Before starting to look at the effects of the dilution genes, not to mention the other genes that affect horse color, it is important to realize that horses, like most mammals, have two kinds of pigment. One, eumelanin, is black, and while some of  the dilution genes may affect it, the kind of brown that produces the chocolate Labrador is not known to occur in horses. The other pigment, called phaeomelanin, varies from rich red-brown to a lighter golden red. We’ll call that red, but that color can also be changed by other genes.

Chestnut horse, white star almost hidden by bridle. Note the way the color remains red or lightens toward the hooves, as well as the mane color.

The three basic horse colors are chestnut, bay, and black. (Seal brown may be a fourth color genetically, but that is still under investigation.) Patterns of white, interspersed white hairs, or dilution may act on any of these colors, as may a general scattering of black hairs through the coat. But these three colors are the base for all horse colors. DNA tests are now available for the genes that produce all of these colors.

Chestnut is predominantly red, including mane, tail and lower legs. The mane and tail may be lighter than the body (often called flaxen, and sometimes with interspersed white hairs) or darker than the body (usually due to interspersed black hairs.) The dark shades of chestnut, called liver chestnut, often have interspersed black hairs over the entire body. Chestnut is due to a recessive form of the same gene, called extension, that produces yellow Labrador Retrievers. Chestnut is recessive to normal extension (which allows black mane and tail) but in contrast to dogs, black can occur in the coat. Recessive means that chestnut to chestnut breedings can produce only chestnut foals, but bay to bay (or bay to black or black to black) can produce chestnut.

Bay horse. Note the black on lower legs as well as the black mane and tail.

Bay horses have red on the body, but the mane, tail and lower legs are black. Interspersed black hairs are again a possibility. In addition, many bay horses have some body hairs (most numerous on the upper part of the horse) which have red bases but black tips. This type of hair, with a band of red on a hair with black tips (and sometimes even black bases) is very common in mammals, and is called agouti. Bay is in fact an agouti gene. and is dominant to non-agouti.

Black is most commonly due to non-agouti. Black horses have primarily black hair. There is a separate gene, called mealy, that can produce lighter shading on the muzzle, though there is some evidence that a similar effect can result from an agouti gene called tan-point. Black is usually recessive to bay–that is, two bay parents can have a black foal, but it would be very unusual (and probably an indicator of the rare dominant black) for two black parents to have a bay foal.

Any of these colors may have white markings, and as long as the markings are confined to face and lower lets, the horses will still be called chestnut, bay or black. A bay, for instance, can have four white stockings and still be a bay. Only the most extreme white markings can hide which base color is present.

I’ll be blogging on more of the horse color genes in the next few weeks. If you want a primer on basic genetics, check out my website on coat color genetics in dogs.

Radio Marketing

#scifi #amwriting Writing a book is just the beginning–the easy part. Marketing it is a whole new world, especially for an academic like me.

The latest is an interview on internet radio, to be broadcast at 4 pm EDT October 30, 2010. I’ll have the mp3 on my website once I get it and figure out how to insert it, but the initial broadcast will be 4 pm EDT, 3 pm EDT, 2 pm MDT, 1 pm PDT and noon Alaska time via the website above.There is a podcast link if you are busy at the time I’m on.

I’ll be discussing Homecoming, of course, but you’ll get a little of the philosophy behind it, as well. Hope you can listen in, if not at the time, then to the podcast or the delayed broadcast accessible on the site.

Firstday (Homecoming Glossary)

FIRSTDAY: #scifi First day of a fiveday. It is considered a holiday at Tyndall, but different religions and occupations take various days of each fiveday as being “special” in some way.

Follow-me (Homecoming Glossary)

FOLLOW-ME: #scifi A person teleporting himself normally brings along anything he is touching (such as clothing) unless deliberately leaving it behind. (A person could, for instance, teleport into or out of an isolation suit.) For massive objects, a “follow-me” circuit will link the object to a small receiver carried by the teleporter, as well as providing the extra energy needed for the teleport of the object.

Screamer (Homecoming Glossary)

SCREAMER: #scifi An electronic gadget that produces a burst of telepathic noise. They can be set for various intensities, and a good telepath can to a certain extent work through one, but not easily or without special training.

Artificial conscience (Homecoming Glossary)

ARTIFICIAL CONSCIENCE: #scifi The R’il’nai literally share in the emotions of others, which they referred to as empathy. Riyan society evolved with the assumption that everyone had this trait. The rare children lacking this ability were considered badly handicapped and treated while young to react as if they felt the pain of others. In severe cases, this could lead to a treated individual actually convulsing or collapsing if he or she caused pain to another, but this was considered better than having one individual disrupt the whole society.

Month (Homecoming Glossary)

MONTH: #scifi A thirty-day period composed of six fivedays. In the Confederation, it has nothing to do with a moon. (Central doesn’t have one, anyway.)

Planet Building 11: Suns and moons all over the place

#scifi Many planets have satellites, generally called moons when they are visible in the planet’s sky. These moons, like most other aspects of a planet, are subject to physical laws. Their apparent color, size, phase, periodicity and the strength of the tides they cause are all linked together.

To start with, let’s assume a planet with Earth-like gravity (which means Earth-like mass and size if it’s rocky) and a moon large enough that self-gravity has pulled it into a sphere. What will that moon (or moons) look like?

First, color. A moon shines by reflected sunlight. We’ve already discussed the fact that the light from just about any star will look white if there is no other color to compare it with, and the same will be true of moonlight. The color of the moon’s surface may have a slight effect, but only if it contrasts sharply with another moon in the sky at the same time. But what kind of contrast could we expect?

Water and free oxygen are very unlikely on the surface of a moon-sized object circling a planet that can be lived on by human beings, so the red iron oxides and blue water of Earth are out. Copper-containing rocks may be blue or green, but given the elemental abundance of copper in the universe it is unlikely that they would be present in such quantities as to color the entire surface. Sulfur is certainly a possibility–it gives Io its pizza-pie appearance—but it is so widespread on the surface of Io because intense volcanism, fueled by the enormous tidal pull of Jupiter, is continuously resurfacing that moon. Moons could certainly be brighter than ours (which is actually about the color of tar) but it is unlikely that they would look any color but white to our eyes.

How about size? Halve the diameter of our moon, while keeping it at the same distance, and it will look half the size in the sky. But putting it twice as far away, while keeping the diameter constant, will have exactly the same effect on apparent size. It will also, however, lengthen the orbital period—approximately the time between successive new moons. Doubling the distance will increase the period by a factor of 2.8.

Any moon will cause tides, and the tidal force will be proportional to the apparent size of the moon and its density. Thus our sun and moon look very nearly the same size in the sky, but the moon has over twice the tidal effect of the sun. Why? Because the sun, being largely compressed hydrogen, is less than half as dense as the moon. A moon the apparent size of ours but with more iron (denser) would produce stronger tides; an ice moon (virtually impossible at our distance from the sun) would produce weaker ones.

Moons have phases because they are lit by the sun on only one side. The phase thus depends totally on the angular distance between the moon and  the sun. In particular, a full moon rises at sunset and sets at sunrise. It will be relatively high in the midnight sky in winter; lower in summer. (This is really marked in interior Alaska, where the fact that the moon’s orbit is not quite parallel to that of the earth gives us times when the full moon, but not the sun, is circumpolar, and other times, in summer, when the full moon stays below the horizon.)

A half moon is always 90 degrees from the sun. A waxing half moon will rise around noon and set around midnight with the round side always toward the sun; the waning half will not rise until midnight. Crescents are always fairly near the sun in the sky. A waxing crescent sets a little after sunset; a waning crescent rises a little before the sun. In either case the horns point away from the sun.

Multiple moons in different parts of the sky will have different phases.

An example? Here’s one, from a trilogy I’m working on:

She opened her eyes to see the room, with a gibbous moon just above the horizon and a smaller half moon much higher in the blue morning sky.  Sunlight from the opposite window lay on the wall, and when she took a step forward she saw that a shabby-looking city lay below her, between the building and the prairie beyond.

Suns and moons all over, but they are in proper relationship to each other.

Accelerated healing mode (Homecoming Glossary)

ACCELERATED HEALING MODE: Under normal circumstances, the body reacts against rapidly dividing cells. A Healer can temporarily suppress this reaction, allowing healing to take place much faster than normal. However, this state is not normal and can lead to cancer if not reversed within a few days.

Calendar (Homecoming Glossary)

CALENDAR: #scifi The Confederation calendar has slightly more than 364 days a year, with 4 of those days and whatever leap years are needed being considered outside the twelve 30-day months. “Day” and “year” are based on Central’s orbit and rotation rate, so the Confederation calendar does not quite match that of any other member planet of the Confederation. Most member planets have their own calendars, though year and day lengths are close enough to Central’s (and Earth’s) that matching is possible over a few fivedays’ time. The Confederation calendar is used to synchronize time across the Confederation as well as being the usual calendar on Central.