A Note about Sugarbush Draft Horses

I see it over and over again, and no matter how many times it's said, it's still wrong. "Sugarbush Drafts are just an Appaloosa Draft Cross". Uh.... no. The Sugarbush Draft Horse was a breed created many years ago in Ohio. While the initial cross was made using Percherons to Appaloosas, in the many generations following, the breed has been solidified into a consistent type. Saying these horses are "just" a draft cross makes as much sense as saying that AQHA horses are "just" a Thoroughbred cross, American Cream Drafts are "just" a dilute Belgian, or that Morgans are "just" a grade.

Friday, July 30, 2010

Frame Over and Overo Lethal White Syndrome (OLWS)


For those who have been keeping up, I apologize for the delay in this posting.  But, here it is, the basics of frame white overo! And actually, it's just the basics.

Frame white earns its name from the dark "frame" around the white areas of the horse, like on this stallion.  While many types of white markings are often thrown into the "overo" category, this is the main pattern associated with the name.  Frame white causes a horizontal type appearance to the body spots, and horses with this type of patterning often have asymmetrical face markings.

Horses showing frame white patterning are always heterozygous for the gene (Oo).  Horses who are homozygous recessive (oo) are solid (or at least do not show frame white) and horses that are homozygous dominant (OO) are non viable.  Homozygous dominant frame white horses exhibit what is called Overo Lethal White Syndrome, or OWLS.

To put it simply, homozygous dominant horses (OO) are born solid white, and have a non functioning gut.  How does a color gene affect the horse's intestines?  Well, nature likes to be efficient, and in reality color is often a bi-product of the genes real function, and not the main purpose of the gene.  We often relate the genes' functions to their most obvious result - coat color, just because that is what is easiest to see.  In the case of frame, it's not easy to see the intestines of a horse, but the eye catching white markings are hard to miss.

OLWS foals usually will die within 72 hours of birth, if not euthanized before.  The nerves that work the gastrointestinal system do not develop properly, and these poor foals are born with contracted and occasionally deformed intestines.  Surgery to remove or bypass the affected area has never been successful.

Word of warning here, not all solid white foals have OLWS.  Things like dominant white, maximum sabino, or even a surprise cremello foal could easily be misdiagnosed as a lethal white. 
The first vet I worked for had what he thought was a lethal white foal.  His overo mare, bred to an overo stallion, produced a solid white filly.  He was devastated, but the filly seemed to be thriving, and passed her meconium. Luckily he took the "wait and see" approach.  I have to note that while I adore Dr. Paul, he is not a geneticist, and he didn't know the difference between the overo patterns.  His mare what a sabino, and the stallion was a frame/sabino combination.  The resulting filly could not have been lethal white, the mare (oo) did not carry the genetics, but because it was an "overo to overo" breeding, lethal white was suspect.  Also, this was almost 15 years ago now, before the problem was well understood.

Frame is an incomplete dominant gene though.  There are 3 distinct phenotypes (appearances) associated with it.  Homozygous recessive horses are solid, heterozygotes show irregular patterning, and homozygous dominant foals die shortly after birth.  The gene is represented with O, for overo, but do not let this confuse you.  Overo is really a group of color patterns which includes frame, splash white, and sabino, as well as a few other more rare patterns like dominant white.

Sadly, I couldn't find much information on minimal frame markings.  It appears that frame can hide easily in other white patterns though.  Many horses believed to be tobaino/splash turn up carrying frame as well.  I know Evensong posted a picture of her mare that hides frame really well. 

This miniature filly is a minimal frame white, DNA tested Oo.  My problem is that she shows classic minimal splash white markings.  Since there is no DNA test for splash white (yet) it is hard to know if there is some interaction between these genes.  Could splash hide frame in certain situations?  Does minimal frame white mimic splash white face markings, but leave the legs dark?  It's hard to know.  Just goes to show that we have so much more to learn about coat color genetics!

Like other pinto genes, there are varying levels of expression for frame white horses.  Frame can be expressed with other pinto genes, such as splash, sabino, tobiano, and dominant white, which means that many horses are not "pure" frame white, and show traits of other pinto genes as well.

Here is a tovero stallion that shows both tobiano and frame traits.
 Note the irregularity of his otherwise typical tobiano blobs. His asymmetrical face marking could be caused by splash white (he also has 4 white legs) or frame.

And this horse is a great example of the asymmetrical face markings typical of frame white horses.
Notice the dark pigment on his topline?  This is where the gene earned its name, with the dark pigment "framing" the horse.  I have to admit here that frame is one of my favorite pinto pattern genes, even though I know so little about it.  While frame white horses are harder to breed for, due to the inability to breed frame to frame (with out risk of losing the foal), or the existence of homozygous frame horses, the results are truly stunning.

And everyone who thinks these horses are beautiful should read EvenSong's post about her experience learning about Lethal White.   EvenSong shares even more information about Frame Overo horses.  Definately worth the read.

Wednesday, July 28, 2010

The beauty of technology

So, I have recently made a facebook page for the Sugarbush Drafts.  Check it out.. I made a handly little widget thingy too (on the left there).

I'm pretty impressed with myself for this.  For those who don't know, I'm really very facebook challenged!  I can't ever seem to figure out how to navigate around, I never know if my updates and such are publishing properly, and the whole concept is a bit weird to me.

But hey.... what better way to get people learning about these horses then facebook, right?


On the downside, I had someone interested in Zire recently.  I was very excited because it sounded like a perfect home for him, but he wasn't quite what she was looking for.  A lovely horse shopper though!  Let me just say, if every potential customer was this open, upfront and honest, the horse market would be amazing!  (Ok, and sellers too, but I'm an honest seller... really!).

At any rate, I added a few more horses to the sales list.  I'm not in a hurry to sell them, but I'm willing to let go of them for the right person.  Everyday something happens that makes me re-evaluate what I'm doing with the Sugarbush Drafts, and how I want to get there from here.  I love all my horses, and wish I could keep every last one, but I also know that many of these would be great additions to other families/breeding programs, and the only way to grow the breed, is to share the wealth (lovely horses).

Now, if I could just find the time to catch up on my research for frame, to make sure I don't spread any lies... then I'll get that pattern posted!

Monday, July 26, 2010

Tobiano, the easy pinto gene

Ok, first off the reason I call these pinto genes, and not paint genes has nothing to do with breed.  Horses with large spots of color are commonly called pintos, regardless of their breed.  So, this includes Paint (APHA) Pinto (PtHA) as well as many grades, a few warmbloods, Tennessee Walking Horses, Missouri Foxtrotters, Shetland Ponies, Miniatures, and well, you get the idea.

Pinto genes are often refered to as genes that cause large white spots on the main body.  Now, as we discussed before, that's not all that they do.  Some pinto genes can cause only face and leg markings when in minimal form.  In fact, most of them can do this.

In other breeds that don't care for pinto type coloring (ApHC, AQHA of the past, and such) these genes are regularly allowed in the gene pool, so long as expression is kept to a minimum.  Let me tell you, appaloosas have all types of pinto genes in their pedigrees, and people love the chrome, until the right combination of genes occurs to express a full blown pinto pattern, and not just some pretty face and leg white.  Suddenly, a breeder is left with a foal that can not be registered.

Of course, I mention Appaloosa because that's the only color registry I'm personally familiar with.  I have to note here that the Sugarbush Draft Horse is a colored breed, but selection is not made by color.  Horses with excessive white are allowed, and the only gene selected against for color is.... Tobiano.

An interesting little tidbit I came across today:  Tobiano was named for the he rescue of Buenos Aires by Brazilian General Tobias during some military event in the 1800s.  I didn't know that and found it rather interesting.

As to how to define Tobiano in a horse?  Well, tobiano tends to cause white legs from the knees (Carpus and Hock) down, but leave "normal" face and leg markings on the heads.  Horses with Tobiano in its minimal form will often have excessively high leg white in comparison to their face markings.  If you see a horse with 4 knee high white socks, but only a small star, then Tobiano is often the cause.

Now, interestingly, the minimal tobiano horses still produce the same as a "typical" tobiano marked horse.  The typical Tobiano will have a "halo" outline to its spots.  Basically it's an area of dark skin that grows white hair, causing a thick outline to the spotted areas.  While a horse with tobiano patterning might have more or less white (amount of white is related to those enhancers and suppressors as well as other genes that aren't well understood yet) they all tend to have a commonality to the type of spotting and location of spots on their body.  Tobiano markings are happy to go across the back, while other pinto markings don't.  Tobiano horses are often seen with a "shield" or dark area on their chest, although horses with higher amounts of white might not have this trait.  Spots on tobiano horses tend to have an oval shape to them. I think of the spots as "blobs of color" on the horse, as opposed to other pinto markings that are more organic and irregular.
This foal is pretty typical of tobiano on a horse.  Note how the white on the neck and hip cross over the back, the foal has 4 white legs, and appears to have a solid head.  White is seen in the tail, which is common with tobiano.
The horse above has those blob type markings I was referring to.  While her blaze makes me suspicious of additional pinto markings, most of what is seen on her body is a typical tobiano appearance.  When compared to the foal above, there are similarities in placement and type of spotting, although the mare is higher on the level of expression then the foal (more white).

As for the genetics of this pattern, well Tobiano is "easy" because it's a simple dominant gene.  A horse has it, or they don't.  The arguement that this gene is incompletely dominant can be made because many homozygous tobiano horses show something called "paw prints" or smaller dots in their white areas.  This is a great example of paw prints.
 Tobinao is a mutation of one of the KIT genes.  That really doesn't mean much to most people, but it's the location of the gene on the DNA.  Now the KIT genes tend to be very very close on the DNA.  The closer genes are to each other, the less likely it is that random recombination will take place between them.  Head hurt again?  Let me put that in simple terms.

When sex cells are produced (sperm or eggs) the DNA is split.  Just before this splitting, the DNA twists up together, and sometimes will flip to the opposite strand.  This is what allows a stallion (or mare) to pass on both his (or her) maternal and paternal traits, while only giving 50% of his DNA.  If this didn't happen, a horse would only pass on EITHER their Sire's traits, or their Dam's traits, never both.

So, If a stallion had a chestnut mom, and a black sire, but he's bay, he would only be able to produce chestnut (with agouti) or black foals... never bay like himself (a combination of dad's black, and mom's agouti).

Anyway, the closer genes are, the harder it is to split them up.  Think of it like trying to cut between knots on a string.  You need a bit of open space to fit the scissors in. If the knots are tied too close, you'd end up cutting the knot, and not the string between it.  Genes are pretty much the same way.

The genes that are so close are tobiano, roan, extension, and a gene for blood type.  The first tobiano tests traced blood type, and judged a horse homozygous based upon the chances of recombination.  This was inaccurate, but the best we could do at the time.  Now, DNA tests are available for the tobiano gene, and a horse that is DNA tested is much more likely to be accurately identified by the test.

Now, because the linked genes are not at the same location, just close, they are still inherited separately.  It IS possible for recombination to occur, but it's rather unlikely.  In other words, the percentage of foals would be skewed to reflect the parent's entire sequence of DNA here, rather then each gene being inherited on its own.  If you have a roan tobiano stallion, (Ee Aa Tt RNrn)  He would likely pass E T RN as a group OR  e t rn. But he would rarely (although still possible) pass E t RN, E t rn, e t RN, and so on.

Also, because pattern genes do not share a location (loci) on the horse's DNA, a horse can have multiple patterns at once.  Roan, rabicano, tobiano, frame, splash, sabino, appaloose... a horse can actualy have them all.  And all of these patterns are built on top of the horse's base coat.

Of course, I'd like to remind you here that pattern genes are actually genes that repress pigment production.  Often when people try to reason out horse colors, they think of laying the white on top of the base coat.  It's actually the other way around.  The horse starts as a clean slate (white) and the pigment cells are spread throughout the body producing coat color.  The color goes on top, but like trying to paint over wax, some pattern genes prevent the color from sticking in certain spots.

Now, hopefully my pinto loving friends out there will correct me if I made any mistakes in this.

AND, time for your test.....


Give me the genome (string of letters) for this horse.  You can use question marks where genes would be unknown.  (Hint: this horse is seal bay)

Sunday, July 25, 2010

Taking a day off for riding and Family

I have really enjoyed blogging about genetics recently, and I hope I am not boring any one too much.  It's also been a great excuse for me to look up and check my facts on a few things.  I love researching.

So, expect to see more information about tobiano on Monday.  Today, I will be enjoying a few ponies, and cooking a steak for my dad.  Ok, I won't be cooking, but I sure will be eating it!

And I'd like to congratulate Heather on THIS:

That's Rose, under saddle!  She looks like a very happy girl (yeah both of them).  Rose has been confirmed in foal to O, and it looks like we will have one more Sugarbush Foal on the ground in 2011!  I'm very excited about all of this.  Congrats Heather.

Saturday, July 24, 2010

Happy Birthday Dadd!

First off, I would like to say Happy Birthday to my father.  He's 39 this year... again.  Thanks for everything Dad, and here's hoping you have a nice and relaxing day!

Dad has always been an inadvertant driving force behind my horsey addiction.  From encouraging me as a child, and driving me all over to get my horsey fix - and I probably shouldn't mention that I think I learned the word horse before I could say "Daddy" - to failing to discourage me as a teenager, by telling me how expensive horses were, and bringing out the rebel in me ("Oh yeah, well I'll show YOU").   Horses have plagued him since... well... the year I was born (and we won't say when that was!).

In 1999, my father acquired his first share in horse ownership, when a crazy owner decided she was going to take back my mare if I didn't pay her off within 24 hours.  Dad ponied up the money for his poor college daughter, and refused to allow me to pay him back the full amount.  Yes, my father owns $5 worth of my old thoroughbred mare, Ash.  And yes, he's listed as a co-owner on her papers with the Jockey Club.  His reasoning?  I can't sell her unless he signs those papers. 

He purchased his OWN horse in 2000.  A fellow boarder at my stable made the mistake of going to an auction.  A chestnut colt ran though, and the only bidder was the meat man.  My friend tossed out a bid, and the meat man stopped bidding, so she came home with a skinny ugly yearling.  A couple of weeks later my father met the colt, and decided he liked the price.  He still says that he bought the horse to keep my mom's horse company....suuuuuuure he did.

Then, in 2005,a string of coincidences occurred.  Jae prompted me to put my string of skills together, and start breeding.  Here's the really strange part... my father encouraged me!  Dad offered to become a business partner, and assist with the start up fees.  Of course, he made me write up the business plan (evil evil man, but that thing has been really useful, in all of its incarnations) and he was rather involved with picking out our first stallion.
 Dad is involved with the babies, and always seems to have a treat in his hand for one of the ponies.  After 3 knee surgeries, he still climbs up on a horse, and wanders around.  He's not the best rider, but he seems to enjoy it, and the horses all adore him. 

And now, in 2010, he has taken a job with a carriage company in Dallas.  He's learning to drive the big horses!  When my father began explaining to me why one horse needs a collar and another uses a breast plate, I had to chuckle.... he still says he's not a horseman.
 So Daddy, here's to you, and all the crap you put up with.  You'd better have a Happy Birthday!

Rabicano

First, Check out the horse.... I found the COOLEST site!  Ok, This site has a function thingy mabob (yep, it's obvious that I'm not technical, eh?) that allows you to click on genes, and see the results of various combinations.  It's not perfect (Appaloosa is ALL wrong) but it's pretty close for base colors.  Just click on the link, or go to http://www.jenniferhoffman.net/horse/equinegenetics.html and check it out.

I can't believe I've never seen this before.  It's cool, and very useful for showing people how the genes stack up on each other's effects.  Granted, I couldn't figure out how to save a picture of a horse with Rabicano, so a seal bay with silver will have to do instead.

Now, Rabicano is a white pattern gene.  This pattern is a roan type pattern, but it's inherited separately from classic roan.  Rabicano is refered to as RB, and it's genetics aren't well known.  Currently we discuss it as if it's a simple dominant gene, but again, no one seems to be positive of that, and I can't find any definitive research on it.  I think this is a case of horse people knowing the trait exists, and no one has gotten around to studying it yet, because it's not THAT popular (i.e. won't bring THAT much money to the university).

So, Rabicano is most often seen as a racoon tail, or a stripped are at the top of the tail.  While there are varying levels of expression, rabicano seems to always affect the tail hairs, resulting in a pattern like this:
With higher levels of expression, ticking, or roaning (although not caused by classic roan) is seen on the rib area and flanks.  The ticking can be dense or light, and in some cases owners never realize that this is a pattern gene at work.  First Picture from here, and second picture from here.

As you can see, the first horse has some scattered white hairs in the flank area.  The second horse though, shows extensive white markings traveling up towards the front legs across the ribs, as well as a very white area on the top of the tail.

Like all pattern genes, Rabicano can be inherited with other patterns.  Yes, it is possible to have Classic Roan with Rabicano, although in some cases it is hard to be sure of this.  The best way to check for rabicano, is to look for the stripes in the tail, because white ticking on the sides can be so minimal as to be impossible to see, or it can be covered up by other white markings such as tobiano, or appaloosa.

Because there's no real knowledge about the genetics of Rabicano, I can't go into inheritance of it.  There is a similar trait called a gulastra plume.  This results in a horse with a white or greyish colored tail.  Here is an example:
To my knowledge, gulastra plume has no genetic correlation to Rabicano.

So, today's test............


What color would this horse be?

EE aa CHch Dd RNrn

Friday, July 23, 2010

Classic Roan

Roaning is the generic term for white hairs intermingled throughout the coat of a horse.  Most people know about blue roans, strawberry roans and such, but there are many reasons for horses to show roaning.

The best known type of roaning is called a Classic Roan.  These horses tend to have evenly (or nearly) mixed white hairs through the body area, with darker heads and lower legs.  Classic roan can be seen on any base coat color.

Now, credit for the picture here.  This is an image that kept popping up in my searches for examples.  I just can't get over how lovely this horse is, and I'm not even a quarter horse fan.  His picture was used for an ad for this website.  It appears that his name is "My Final Notice".  Lovely horse.

Grey horses can go through a state that looks similar to a classic roan, but a grey horse will continue to lose pigment over time and get whiter each year.  There is also a type of roaning associated with appaloosa colors.  This is called varnish roan, and I'll go into it more with appaloosa genetics.

The other well known type of intermixed white hairs is called Rabicano.  Rabicano is best known for the "skunk tail" or "racoon tail" type markings seen with this pattern.  While classic roans have white hair intermingled all over their body, rabicanos tend to have white roaning around the tail and rib area.   Sabino can also cause a roaning type of appearance, but it is often seen with pinto like markings (although not always).

Here is an example of a blue roan horse.  This horse shows the typical lighter body color with darker head and legs.
This horse appears blue because the base coat is black.  From a distance the human eye blends the hair colors to see an overall shade that is somewhere in the middle.  Black hairs next to white hairs results in an overall grey appearance.  When you look at a roan up close, you will see something different. 
The dark spots on the horse above are called corn spots.  Corn spots are usually caused from old injuries (but not always) and the hair regrows in those areas without the intermingled white hairs, resulting in a dark spot.  Roans are most often identified when they shed their foal coat, although in some cases it's earlier and in other later.  Some roans are actually late bloomers, and do not show signs of classic roan until as late as 5 years of age.  This can make it hard positively identify them, since grey can do the same thing. 

Roaning is actually a pattern, not a base coat modifier, because roan prohibits pigment production, as opposed to modifying the pigment produced.  Previously, it was thought that classic roan was lethal in the homozygous state, with homozygous embryos being nonviable, and thus never even born.  This has since been disproven.  First in 1979 with a few Ardennais stallions (a type of draft horse) and later in quarter horses.

The problem with the early phenotype testing (testing based on outside appearance, not DNA) is that multiple types of roans were included, not just classic roans.  Frosty roans, classic roans, rabicano roans... all of these roans were bred together, and the results did not show the typical  1-2-1 dispersal expected with incomplete dominance, or the 3-1 expected with a simple dominant gene.

Let me explain that for you.  When identifying modes of inheritance by appearance of a trait you calculate the percentage of offspring produced and their appearance.  So, lets say I have 100 foals from black to chestnut breedings.  75% of those foals should be black, and 25% of those foals should be chestnut.  With DNA testing we would see that 25% were EE, 50% Ee, and 25% ee, but both the EE and Ee foals would appear "black" and thus grouped into the same category, resulting in 3 black foals to every chestnut.  This 3 to 1 ratio tells us that a gene is a simple dominant gene.

In incomplete dominant genes, you would see a 1-2-1 ratio.  As an example, if you breed a palomino to a palomino you would get 25% chestnut foals, 50% palomino foals, and 25% cremello foals.  This is making it very simplistic, as normally the results are never that perfect.  We often see things like 23%, 56%, 21%, but you can see how that is close.  The larger the group studied (1000 foals vs 100 foals) the closer you get to the ideal percentages.  Of course, the problem is the reality behind testing things like this.... what do you do with all those foals?  Because of that, we rarely have the sample sizes desired for the best testing.

Now, if you do a test like this, and you're using multiple genes with similar appearances, then your results will be all over the place!  Many scientists suspect this is what happened with the first phenotype testing for roan.  We know that rabicano and classic roan are inherited independently of each other, so this would skew the results.

Now, classic roan is a simple dominant gene, and is referred to with the symbol RN or rn (yes, that's an r and an n).  I have often seen the dominant copy also referred to as Rn.  The question of how much roaning a horse gets, well, that is determined by those enhancers and supressors we discussed yesterday.  Sabino, splash, base coat color, and other enhancing factors can cause a horse to have more white hairs, while the lack of them, or restricting base coat colors (such as EE) can cause a horse to be minimally roaned.

As a comparison, look at this minimal roan and compare it to this extreme roan


Now, like I said, roans come in all colors.  Here are a few examples:

Red Roan












Bay roan













Buckskin Roan

(and isn't he just adorable?)












Palomino Roan













Of course, I used many blue roans (classic roan on black) as my initial examples, simply because it's so easy to see.  Also, all links above lead to the horse's websites, many are breeders.  (I seriously recommend the website for the buckskin roan, some LOVELY mini horses there, in all colors.)

Now, none of the horses below are roans.  Today's test!  Can you guess what patterns/colors cause these horses to have a roan-like appearance?  It's a bit unfair, because we haven't covered a lot of these colors yet, but hopefully it's more fun then just guessing letters!

12 

And bonus points for those who can write the genome for the horse's color (base color only is ok).

Thursday, July 22, 2010

White face and leg markings

One of the most common types of patterns seen on horses are face and leg markings.  There's also a bit of a debate surrounding these markings.  Some say that Sabino is present with any face/leg marking, while others say that many are "birthmarks" and that they just happen.

I'm not sure a study has ever been done to determine who is correct.  We do know that face and leg markings are inherited, and that sabino (which is actually a group of genes) causes certain characteristics to be seen on face and leg markings.  We also know that other genes affect face and leg markings as well, such as splash and Overo (OLWS). I think that much of the sabino debate is due to people wanting their horse to have some "cool" pattern, and the recent acceptance of excessive white in many breeds from Arabians and Thoroughbreds to the white rules in AQHA.

Certain types and locations of these markings are considered normal.  Socks, blazes, stars, and stockings are all easily accepted markings on a "solid" horse.  Then you have something like this filly shows.  Her blaze is irregular, and even has a hole in one area of it, and a displaced section of white on the opposite side.  This is Soliloquy, a Stonewall Sport Horse filly whose name I usually shorten to Soli.  Her dam has both sabino and splash (black mare shown below), while her sire carries sabino.  Soli's markings show mostly traits of sabino, but there are a few signs that show she is also carrying splash.

Ever wonder how to tell the difference?

Sabino markings tend to be pointy.  Sharp areas on blazes and socks that point towards the belly.  Also, white on the lower lip is a big indicator of sabino.  The chestnut shown below has classic sharp sections around his nostrils, and the black has obvious white on his lower lip.  Both horses are suspected to have minimum sabino.
For many people these markings look perfectly normal, and they are.  But splash tends to cause face markings that are heavier on the bottom, and often rounded or apron shaped.  Here are a few examples of splash blazes.
Granted, both mares above are giveaways because of those blue eyes - which is most often a trait of splash.  You can also see though, that while the blazes are very different, both are heavier on the bottom, and are mostly smooth shaped.  Below is a mare with a large face marking showing traits of both sabino and splash.
This is Jinx, one of my foundation Sugarbush mares.  On her left side (the first image) she shows classic sabino signs, including the blaze that goes under the lip, and a few subtle hints of splash, such as the width of the blaze and rounded nature of it.  On her right (second image) she has a "dipped in paint" appearance that is often seen with splash, and is always present when splash goes under the chin.  Also notice the sharp pointy effect around her eye, and in her cheek area?  Those are signs of sabino.  Jinx is a good example of how common markings can give us clues as to minimal white patterns carried by a horse.

Then there are leg markings.  Sabino leg markings are pointy (see a pattern here?) and usually are higher towards the belly.  The only horse I have that shows this carries both sabino and splash, but I think you can get the idea.  Yes, she's also very pregnant in this picture.
On the other hand, splash markings tend to be even on all 4 legs, or close to it.  The seal bay mare shown below has even socks, but they all point backwards.  This is occassionally seen on both splash and sabino horses.  With the prevalence of sabino in appaloosas, it's reasonable to assume from the sharp tops of her socks that the seal bay mare also carries sabino in addition to her splash.
On the other hand, not all splash horses have 4 white legs.  Arden, shown below, only has 3 white socks, which are close, but not perfectly even.  She shows no obvious signs of sabino, but again, due to the breed, we can't rule it out.
But what about horses who don't have that much white?  Here's a mare with no leg markings, and only a small amount of white on her forehead:
Her appaloosa colored colt has almost the exact same white marking as well, and neither has any leg markings.  Could these be from embryonic development?  In other words a birth mark?  Science has yet to prove it, although neither she, nor the foal show signs of additional effects of other white patterns.

As for those "other effects" well, genes like sabino, splash and frame (commonly called frame white, or overo) have an effect on other white patterns.  These are called "enhancer genes".  It is a well documented fact that horses with excessive white face and leg markings tend to show more white in their patterns as well, both pinto and appaloosa patterns.

Base coat color also plays a role.  Dominant extension (E) is a suppressor of white patterns, while recessive extension (e) is an enhancer.  What does that mean?  Well, a horse that is Ee will have a smaller blanket then a horse that is ee, and a horse that is EE will have an even smaller blanket then the heterozygote.  Agouti is an enhancer gene, and it's effects have been documented even when the gene is hidden.  A horse with the genome ee AA will have a larger pattern then a horse with the genome ee aa.  To make it somewhat easy to remember, we often say that black supresses the most, then bay (a little suppression and a little enhancing), then chestnut. 

These suppressors and enhancers will become important when I talk about appaloosa color genetics.  There are MANY genes that have a suppression or enhancing role in color, and not all of them are known.  In some cases we know that certain family lines, or breeds have "suppressors" but we don't know exactly what causes it. 

This is why genetics tends to get so confusing.  There's so much going on at the same time, and genes can have multiple roles.  In many cases people ignore the supression and enhancing traits, and simply work on the basic genetics of the coat color, but if you want to breed for a very specific pattern (such as minimal paints, or leopard appaloosas) then these additional effects must be taken into consideration.

Many of the same genes that cause face and leg white markings can also cause pinto patterns with a "louder" expression.  Splash is most commonly seen as face and leg white, but is most commonly associated with high chrome horses.  Frame is ususally expressed as a pinto pattern, but can "hide" in face and leg markings only.  These pinto patterns being expressed as only "normal" white markings are often refered to as "minimal" (insert type of pattern).  Such as a minimal splash, or minimal frame.

Now, for your test......

What pattern genes would you suspect this foal of having?

There are 3 patterns at work here.  Lets see who can guess!

Wednesday, July 21, 2010

The basics of white patterns

The first thing you need to know about patterns is how they happen.  For various reasons (depending upon the genetics) horses have areas with out pigment.  This can be anything from face and leg markings to solid white horses.

My father used to always ask me jokingly, "Are Zebras white with black stripes, or black with white stripes".  Once I got into genetics, I was able to answer that question.  Zebras are black with white stripes like this picture shows.

The reason is that white markings are actually areas where the pigment production is inhibited.  This means that those cells still have the code for the horse's (or equid's) base color, but something prevents the color from being produced.  That "something" could be many different things, from specific genes to outside factors.  If you keep in mind that a foal starts as a single cell, and as it develops that cell divides, and then those cells divide, you can see how early cells will end up far from other early cells, but later cells will be close to each other.  When the embryo is only 2 cells, one might end up at the tip of the nose, while the other will be the tip of the tail, but in a near term foal a new tail cell will be next to a new tail cell.

Genetic decisions (which genes are activated) are altered through out embryonic development.  Cells are "triggered" to be skin cells, or heat cells, hair cells or hoof cells, depending upon many super technical bio-mechanical things.  Never fear, I won't dork out on those, but it does help to have a basic grasp of this phenominon to see why patterns vary so widely!  Specific triggers can cause genes to be activated, and changes in the body to occur.  An example of this is how a newborn takes it's first breath, but before that the baby gets oxygen through the umbilicus.

First of course, the DNA coding is the "blue print" of what will happen, but just like in construction, things don't always go as planned.  Things such as temperature, position (is the foal pressed against the uterine wall) gestational time, nutriton, and a myriad of other factors all have their role.  A good analogy for this is such construction problems as: expansion of materials in heat, misreading the blue print (yes, this happens in DNA too), and poor building supplies.

Here is an example of some face markings from clones of Smart Little Lena.  These horses have exactly the same DNA, but the difference in markings is due to "external" factors like I mentioned above.  No, we don't always know what did what, but examples like this allow us to take steps to figure it out.
You can see that all of the clones have a similar "feel" to the shape of their blazes, but some have more, and others less white.  The third foal's blaze curves to the opposite side as the donor's (original horse's) blaze!

There isn't a more perfect example of the difference between nature and nurture then clones.  Nature includes DNA, while nurture includes just about everything else.  Each of these foals had a different surrogate dam.  Differences in the mare's average body temperature, location of the foal in utero (right horn, left horn, lots of room or cramped in there) all can change things even though the DNA is the same in each one.

Head hurt yet?  Yeah, it gets worse.

Now, pattern genes basically code for pigment to NOT be produced.  Because of the way the foal's cells develop while it's a fetus, this results in pigment cells being next to similar pigment cells.  Think of a paint horse.  Big blobs of color and white are caused because of this.  Also, the path of cellular development can cause patterns to appear.  You can often see the cellular pattern in leopard appaloosa colored horses like this guy:
For everyone drooling right now, that's Mystic Warrior, a rather popular 3/4 Friesian foal who caused quite a stir and then people lost interest when they learned that he's grey.  His spots show just how the cellular motion during development happens, from the spine down, and across the body.  You can almost feel that his spots are "running" like wet paint.

All horse markins will be affected by that.  This is why you don't see sideways blazes, or appaloosas with only a spotted area on their heads.  It's all about what cells are first and which are last.  In explaining patterns over the next few days, I will refer to this migration of cells, and how some things depend upon external factors to get more "bang for the buck".  Appaloosa is one of them.

Also, just a bit of trivia for you:  This pattern of migration is also why sooty tends to be top down, pangare tends to look like it comes from the bottom um, and why agouti pushes the pigment to the points.  For me, learning about cellular migration was one of those things that made everything else fall into place.

Again, if I've lost you some where and you feel like your head is about to explode, please feel free to email me.  I will explain things in different ways, I'll try over and over.  I know many people are very interested in horse colors, but genetics don't come easy to them.  If you want to know, but don't want to feel selfconscious, simple send an email to me at:  heather@ironridgesporthorses.com

Today, I only have an opinion question.  While digging up the clone pictures, I saw many discussions based around breeding to a clone.  Some people commented that because a clone might not have the same performance ability, they wouldn't think about it.  Others would if only their registry would allow it.  So, would you, or would you not ever breed to a clone (assuming you were wanting to breed a horse)?  Why?