(no subject)

[which_chick]

Old grocery budget: $1544.32
Amount spent (Saturday, for cake): 16.94
Amount spent (mcD's fast lunch): 1.89
New grocery budget: $1525.49



After work today I played horse, which was fine. I also went over to Odie's to see what there was to see. Now, I'd considered going home and getting my camera before going to play horse in case there was anything worth taking pictures of, a reasonable possibility because the broodmares are huge, gravid, and surly. They're due NOW, it being springtime when there is a miracle every day. However, I decided against getting the camera because I live in a gravitational well. (It looks like a valley.) If I head home after work, I do not come back out of the gravitational well very easily. It's too easy to start supper and hit the internet and so forth. I do a lot better if I just go play horse directly from work and avoid the gravitational well. That's why I didn't have a camera. Your loss, because there was a brand-new (born today) black and white tobiano filly (a black-and-white spotted girl horse baby) from Sketch (solid bay, four two white socks and a blaze) and Skoal (chestnut and white tobiano pinto).

Now, how did we get a black-and-white tobiano baby from a solid bay mare and a red-and-white tobiano stud? As it happens, I bought an expensive and complicated (but very explanatory) book titled Equine Color Genetics by a man named D. Phillip Sponenberg, DVM, PhD for JUST this sort of question. (I can see you rolling your eyes from here. Quit it. This will be good for you. It's educational and detective-like and all kinds of interesting.)

Tobiano pinto-ness (whether or not the horse is spotted white-and-some-other-color in a relatively typical pattern that is not germane to our discussion.) is a dominant gene we can call T. There is a recessive t, which is what most solid-colored horses have and also what some other spotted horses have because they have a different kind of pinto-ness like, for example, frame. Anyway, if you have a TT or a Tt, the horse phenotype is generally a tobiano pinto, which you usually can tell by looking at the horse. Sometimes horses only minimally express their pinto-ness and can "pass" for regular solid colored horses. Other times, pinto horses may have active frame, sabino or splashed white pinto-ness occuring at the same time as the tobiano-ness and that can cloud the issue (there are about four kinds of pinto genes, all pretty much independant so that you can have a horse with one or more pinto genes expressing) somewhat. Usually, though, you can tell tobianos by looking at them.

Unlike the gene for roan (another color feature), homozygosity for tobiano pinto-ness (TT) is not fatal. (We know that RR is fatal because we don't get the proper ratio of foals when breeding Rr to Rr. For that breeding, there should be 25% rr, 50% Rr, and 25% RR offspring (looking at 'em, we should see 25% plain, 75% roan babies), but what actually gets born is 1/3 plain babies and 2/3 roan babies. From this, we can reasonably assume that RR simply doesn't get born.) Anyway, horses that are homozygous tobianos only make tobiano babies because it's a dominant gene. Now, Skoal, our pinto horse in the above example, is not a homozygous tobiano. His mother was Careless Star (we called her Snuffy), a purebred Arabian. Arabian horses do not come in tobiano. That's not an available breed option. Every single purebred Arabian horse on the planet is tt. He'd have gotten a t from his mother and because he IS a tobiano, he got a T from his father. So, Skoal is Tt.

Sketch is Xt on the tobiano front. Her father was a registered arabian horse (so tt) and her mother was a tobiano half-arab with one purebred Arabian parent (so Tt, like Skoal). Sketch looks mostly solid-colored, but she's got high white (white on the legs above the knees or hocks could possibly be a minimal expression of tobiano-ness) perhaps I should LOOK at the damn horse before thinking I know what she looks like. She's not got high white. She's got fairly average white, front feet only. I keep thinking she has more white than she actually does, and I'm not sure why. Ah, well. It is not possible to tell TT horses from Tt horses by how flashy the coloration is. It doesn't work that way and Sketch hasn't had any tobiano babies to solid-colored studs yet, so we're at a dead end here on Sketch's genotype. It doesn't really matter because we've already found a plausible pathway for the tobiano-ness. It's a dominant gene, Skoal's got it, and so our work here is done.

Now, about the black. Bay, chestnut, and black are base colors. They are not overly simple because they're controlled by two pairs of genes, called the Agouti locus and the Extension locus. (I don't automatically know this crap. It comes from the book. I'm summarizing.) The Agouti locus controls the location of black coloring in horses that express black coloring. The Extension locus determines whether or not the horse expresses black coloring. Most other horse colors are derived from these basic colors of bay, chestnut, and black by other genes that dilute, spindle, fold, or mutilate the colors further. Since we're not dealing with a palomino or a chocolate silver filly colt, I am not going to discuss dilution genes.

A -- dominant Agouti locus. Black restricted to points (lower legs, mane, tail)
a -- recessive Agouti locus. Black is not restricted
E-- dominant Extension locus. Horse expresses black coloration
e -- recessive Extension locus. Horse will not express black coloration

Clear? Let's put it all together. The following are the options for base horse colors:

Ee or EE -- horse expresses black coloration. Horse will be bay or black, depending on the Agouti locus.
Aa or AA -- the color black is restricted to points. IF BLACK IS EXPRESSED (see Extension locus), horse will be bay
ee -- horse will be chestnut
aa -- horse will be black IF BLACK IS EXPRESSED (see Extension locus)

What we know about Skoal and Sketch:

Skoal is a chestnut horse. He is therefore ee. We do not know, by looking at him, what his Agouti locus looks like.
Sketch is a bay horse. Therefore, she is EX (black is expressed) and AX (black is restricted to points).

Now, we look at this black-and-white filly colt. She's black. Therefore, she is aa. She is expressing black coloration, so she is Ee (Skoal is a chestnut and therefore only has e to give). And, not that we're still on this, but she's a freaking tobiano so she's TX (we're still undecided on Sketch's status).

From this, we can see that Sketch has to be Aa, or she'd not be having a black baby. Skoal also has to have aX -- we don't know the other because black is not expressed on him due to the ee thing. We can't tell from one black baby whether he's aA or aa.

So. Now we know, from the baby, that Skoal is eeaX and that Sketch is EXAa. Neat stuff, isn't it?

You, there in the back -- I can see your eyes glazing over, dude. This sort of thing is important to people who raise horses because, for reasons unknown to me, people pay more for horses that are pinto or black or buckskin (currently fashionable) or whatever. You don't RIDE the freaking color, but people pay more for it. For horse people, understanding how the color works is money in the bank. For the rest of you, it's good mental exercise.

Comments

[which-chick.livejournal.com]

The thing is that the cart pullers are generally of a sanguine and sensible disposition. They're bred for it because they're big enough (my friend's ex-husband's people raised percherons) to kill a man easily. While you get a bigger horse if you ride drafts, you do not get more horse. I got me aplenty horse, I do. She eat you for breakfast. Some days she eats me for breakfast.