Pearl: a Palomino Complication

Sorry, I do not have a single photo of a pearl–just haven’t been able to find one. Sponenberg doesn’t, either. You’ll have to go with the descriptions.

Last week we discussed palomino as if there were just two forms of the gene associated with palomino color: cream and non-cream. The whole story is a little more complex, but I’ll have to introduce some genetic terminology to explain it, even though I’ve used the terminology, without explaining it properly, several times already.

The three new words we’ll be using are locus, allele and wild–type.

Locus means place in Latin, and it originally meant a place on a chromosome. Since genes code for proteins and are now known to be a little more complex than just the place on the chromosome, it now means the particular protein coded for.

There can be slightly different forms of a protein having the same function, and the different stretches of DNA (genes) that code for these slightly different forms are called alleles. Using this terminology, every horse has two alleles, one from each parent, at each locus (plural loci.) Last week we discussed two alleles, cream and non-cream, at the cream (C) locus.

The complications come from the fact that there are in fact three rather than just two alleles at the cream locus. Each individual horse can have any two of these three alleles. To avoid confusion, I am also going to introduce the term wild-type for the gene assumed to be the “normal” allele at a locus in the wild ancestor of a domesticated animal. What we called “non-cream” last week is in fact the wild-type gene that gives normal full color.

(Note that the wild ancestor of the horse is not the “wild” horse of the West—these are in fact feral, descended from domesticated stock. The only true wild horse alive today is Przewalski’s horse in Asia. The Tarpan in Europe was also wild, but became extinct in the 19^th century.)

Using our new terminology, the cream locus has three alleles: wild-type, cream, and pearl. Pearl was recognized quite recently, and it has a very low frequency except in a few Spanish and Portugese breeds and their derivatives. It could be considered a weaker allele than cream, as it has less diluting effect on the coat.

A horse with one wild-type allele and one pearl allele will look very much like a wild-type horse—chestnut, bay or black depending on what genes are present at other loci. A very close look will show skin slightly lighter than normal, or with small pale spots.

A horse with two pearl alleles will have the red pigment diluted only slightly more than would be expected for a horse with one cream allele and one wild-type allele. Black pigment, however, will be diluted much more than is the usual case for a horse with one cream and one wild-type allele. Thus a bay with two pearl alleles at the cream locus dilutes to tan or gold on the body with chocolate mane, tail and lower legs. A chestnut becomes virtually identical to a pumpkin-skinned palomino (technically gold champagne.) And a black becomes a grayish tan with chocolate mane, tail and lower legs. All of these colors appear very similar to those produced by a single dose of the champagne gene, which is a completely different gene at a different locus, but give very different breeding results. Luckily there is a DNA test for pearl.

If a horse has one pearl allele and one cream allele, the resulting color will be cream, usually slightly darker than the cream resulting from two cream alleles (cremillo, perlino or smoky cream.) In particular the eyes are generally blue or amber, and darker than those of cream horses with two cream alleles.

As I mentioned before, there are a number of different ways of diluting horse color, and when two or more at different loci are combined some very odd colors can result and it may not even be possible to tell what genes are present—or what colors can be produced—without DNA testing.

Next week I’ll consider linebacked dun—one of the few horse genes where the wild-type allele is rare today in many breeds.

(If anyone has photos I could use to illustrate some of these horse coat colors, I would really appreciate them.)

Jarn’s Journal day 390

Songbird has decided I need new clothes.

Not that I really need them for warmth, unless I go out at night. It cools off fast in the dry season. But there are an awfully lot of thorny plants, and while I don’t sunburn easily, I do sunburn. And the few clothes I had with me are falling to pieces.

That didn’t stop Songbird from close examination of my one-piece shipsuit (or what is left of it) and my woven tunic. Or my crude shoes, for that matter.

She herself is wearing a kind of tunic made of two gazelle skins, beautifully tanned, fastened together at the shoulders and sides. I am not sure whether the purpose is protection from thorns, a sunshade, or simply local cultural mores – I didn’t get a very close look at the females of her people. The men, at least when running down game, wear very little.

But this morning Songbird presented me with a new tunic. It is very coarse of weave, but it is woven – much like the baskets she has woven to hold foodstuffs. It seems to be woven all in one piece, like the baskets, but of softer fibers than grass. When I asked her what the fibers were, she showed me one of the plants she has asked me to gather for the seeds. She then explained that when allowed to soak in water, the fibers could be separated from the stems. Her people use it only rarely, because of the work involved, but she thought that since I am a god it would be appropriate for me.

I have given up on trying to convince her I am not a god.

Pearl: a Palomino Complication

This post has been reissued here.

Last week we discussed #palomino as if there were just two forms of the gene associated with palomino color: cream and non-cream. The whole story is a little more complex, but I’ll have to introduce some #genetic terminology to explain it.

The three new words we’ll be using are locus, allele and wild–type.

Locus means place in Latin, and it originally meant a place on a chromosome. Since genes code for proteins and are now known to be a little more complex than just the place on the chromosome, it now means the particular protein coded for.

There can be slightly different forms of a protein having the same function, and the different stretches of DNA (genes) that code for these slightly different forms are called alleles. Using this terminology, every horse has two alleles, one from each parent, at each locus (plural loci.) Last week we discussed two alleles, cream and non-cream, at the cream locus.

The complications come from the fact that there are in fact three rather than just two alleles at the cream locus. Each individual horse can have any two of these three alleles. To avoid confusion, I am also going to introduce the term wild-type for the gene assumed to be the “normal” allele at a locus in the wild ancestor of a domesticated animal. What we called “non-cream” last week is in fact the wild-type gene that gives normal full color.

(Note that the wild ancestor of the horse is not the “wild” horse of the West—these are in fact feral, descended from domesticated stock. The only true wild horse alive today is Przewalski’s horse in Asia. The Tarpan in Europe was also wild, but became extinct in the 19^th century.)

Using our new terminology, the cream locus has three alleles: wild-type, cream, and pearl. Pearl was recognized quite recently, and it has a very low frequency except in a few Spanish and Portugese breeds and their derivatives. It could be considered a weaker allele than cream, as it has less diluting effect on the coat.

A horse with one wild-type allele and one pearl allele will look very much like a wild-type horse—chestnut, bay or black depending on what genes are present at other loci. A very close look will show skin slightly lighter than normal, or with small pale spots.

A horse with two pearl alleles will have the red pigment diluted only slightly more than would be expected for a horse with one cream allele and one wild-type allele. Black pigment, however, will be diluted much more than is the usual case for a horse with one cream and one wild-type allele. Thus a bay with two pearl alleles at the cream locus dilutes to tan or gold on the body with chocolate mane, tail and lower legs. A chestnut becomes virtually identical to a pumpkin-skinned palomino (technically gold champagne.) And a black becomes a grayish tan with chocolate mane, tail and lower legs. All of these colors appear very similar to those produced by a single dose of the champagne gene, which is a completely different gene at a different locus, but give very different breeding results. Luckily there is a DNA test for pearl.

If a horse has one pearl allele and one cream allele, the resulting color will be cream, usually slightly darker than the cream resulting from two cream alleles. In particular the eyes are generally blue or amber, and darker than those of cream horses with two cream alleles.

As I mentioned before, there are a number of different ways of diluting horse color, and when two or more at different loci are combined some very odd colors can result and it may not even be possible to tell what genes are present—or what colors can be produced—without DNA testing.

Next week I’ll consider linebacked dun—one of the few horse genes where the wild-type allele is rare today in many breeds.

(If anyone has photos I could use to illustrate some of these horse coat colors, I would really appreciate them.)

Ruby (Homecoming Glossary)

RUBY: #scifi Marna’s pet tineral. She is a bright red jewel, just old enough that her wings will no longer support her. She is descended from the four tinerals Marna initially took to the isolation satellite.

The Four Horsemen of the Apocalypse

Domestication is a mutual process—the plants and animals domesticated historically have met us halfway.

We and our domesticates have entered a kind of symbiosis—both we and they benefit, at least in numbers.

Plant and animal domestication was the first step toward civilization.

There are only two ways of increasing agricultural yield: Increase the amount of food produced per acre, or increase the amount of land farmed.

Once domestication occurred, we were locked into a positive feedback loop between food production and population. But a positive feedback loop is inherently limited and unstable. Are we approaching a crash?

I’ve been taking a Teaching Company course on DVD for the last couple of weeks, and I have to say it’s one of the best I’ve taken so far. I’ve always been interested in the process of domestication, especially since it became clear that the early agriculturists were generally less healthy than their hunter-gatherer ancestors. How did wolves become dogs? Who first thought of riding a horse? Did riding come before or after driving? And are cats really domesticated, or did they domesticate us?

The course is “Understanding the Human Factor: Life and Its Impact” by Professor Gary A. Sojka, but it’s really about human impact. I can’t say it answered all of my questions, or even asked them, but it did a good job of summarizing our current state of understanding, and of steering a middle course between “domestication is a sin and all domesticated animals should be returned to the wild” (most would not survive, and we probably wouldn’t, either) and “animals have no feelings and were put on this world solely for our use.” There are fewer moral problems with domesticated plants and microbes, though even here there are quandaries. How dangerous are monocultures, for instance? Or reliance on a small number of closely related varieties? (Think the Irish potato famine.)

If I have an argument with Professor Sojka, it is that he is too optimistic about the future. This may be appropriate for a college course, but I don’t feel enough sense of urgency. Yes, some people—a small minority even in the West—are beginning to think about long-term sustainability. (The politicians aren’t, by and large.) But the major problem—a population that is rapidly outstripping the carrying capacity of our planet (if it hasn’t done so already)—has become a taboo subject for serious discussion.  “The demographic transition will take care of it.” But will that happen soon enough?

Historically, our population has been kept in check by the Four Horsemen of the Apocalypse. Famine. War. Disease. Death by wild beasts—today, accidental death of all kinds. All of these are premature deaths—death by old age simply is not mentioned. Today, we tend to regard such deaths—those of the young—as particularly tragic. We fight them in every way we can—and in many ways, we’ve succeeded. What we’ve forgotten is that every person born dies eventually, and to reach sustainability we have to reduce the number of people being born until it balances the number who die. Otherwise the four horsemen will eventually increase the death rate to match the birth rate—or more.

Food and energy both rely on sunlight—the sunlight that falls on the earth today and the sunlight that fell hundreds of million years ago, and is now stored in fossil fuels. I group food and energy for several reasons. Fertilizer. Biofuels. Pesticides. Transportation. Pumping water to where it is needed for crops, in some cases pumping down water that has been in storage since the ice age. All of the advances that have allowed us to hold back that horseman ultimately rely on those fossil fuels and fossil water, or plan to replace them with agricultural products. And fossil fuels are becoming increasingly risky to exploit—look at the BP oil spill.

But an increase in agricultural output to match the increase in population means more efficiency—which we are obtaining today largely through fossil fuels—or more land in agricultural production. There is only so much land suitable for agriculture, especially if we want to keep the ecosystem services we depend on going. And one of the oldest causes for war is the desire for more land.

Disease? In part that ties back to our methods of food production, as well. Certainly much antibiotic resistance can be linked to the widespread use of antibiotics in animals, and many diseases that started out in animals have crossed over to human beings. I find it interesting that all of the great world religions, many of them very pro-natalist, trace their origins to early city dwellers. Disease can spread rapidly among city-dwellers. In fact until the last century or two, urban areas were dependent on immigration from the countryside to maintain their populations. Having many children was important to these early city-dwellers—most of their children would die before having children themselves. That’s not true today, thanks largely to public health improvements—but the mindset and the religious imperative remain.

All living things—plants, animals, and human beings—are driven to reproduce. In our case, that deep-seated drive is reinforced by religious and social pressures. We claim we have a right, even a duty, to reproduce. But do we? Not in nature. Nature says the “right” to reproduce must be earned. It’s a lesson I hope we can learn before it is enforced by the Four Horsemen.

The Bargain

Long ago and far away
We made a bargain,
Your forefathers and ours.
One could find game, sharp-nosed, keen-eared, alert to every breeze.
One had spears to kill in safety.
One too often died beneath defending hooves
One too often found no target for his spears.
So we made the bargain:
One to find and one to kill, and the meat to share.

The years passed, and the bargain changed:
Tend our flocks.
Fight our wars.
Pull our sledges.
Guard our children,
Lead our blind.
Amuse us.
Love us, when all the world has abandoned us.

And on the other side, the same:
Share the food.
Share the fire.
Share our lives.

Wolf that was, how can I break the old bargain now?

Dot