Ticking along to roan

Next up, roaning patterns!

Roaning is generally defined as areas (up to and including the whole horse) where the horse's base coat color is evenly mixed with white.  Unlike grey and varnish roan, the white hair is usually present when the foal is born, and generally the horse will keep the same amount of white or get darker, not lighter.  A horse with roaning may appear darker in the roan areas in winter and lighter in summer, but the amount of white isn't actually changing as the seasons do.

Classic roan or true roan is written in genetics as rn (off) and Rn (on), and it's a dominant gene - one copy shows the roaning.  The test for roan is... weird... in that it's not testing for the exact gene itself; they haven't identified it.  But they have identified some markers in other places in the DNA that indicate that whatever gene it is is turned off or on and whether one or both copies are on in certain breeds of horse.  The only public test available is for horses with Quarter Horse and Paint ancestry.

The horse's entire body will be roan, although the head, legs, mane, and tail will have much less white than the body.

Red roan. From Wikipedia.

Bay roan. From Wikipedia.

Blue roan. From Wikipedia.

The three most common versions of roan have their own names: chestnuts are red roans (they used to be called strawberry roans, which is the version I learned as a kid!), bays are bay roans (but used to be red roans), and blacks are blue roans.  From there, there don't seem to be specific names, just a color with roan after it.

I've heard that combining true roan and varnish roan doesn't go the way you'd expect - in other words, probably doesn't mean more roaning - but I've never seen an example, so I can't say for sure!

One of the other distinct characteristics of true roans is that they'll have what's called corn spots.  Those spots are places where the horse's skin was damaged somehow; instead of growing back roaned, the spots will grow back the base coat color.

The examples above are pretty clear-cut roans, but it doesn't have to be that way.  Sometimes roan is really, really subtle.

Minimally roaned chestnut, from (oh god) the second year I was taking lessons - 1993 or 1994 - so apologies for the crappy quality.  Actually makes her look more roan than I remember!

One of roan's close relatives is rabicano.  This is one of those patterns that we can see - we can even see that it seems to be dominant - but geneticists haven't discovered the actual gene for it yet.  They do know it's not the same genetics as true roan, though.

Where true roan affects the horse's whole body, rabicano affects the flank/barrel area and the tail preferentially.  It also tends to be more expressed on chestnuts than other colors, although it can and does appear on any color.

From Wikipedia.

With extreme expressions of rabicano, the ribs may be striped (as in the photo).  In minimal expressions, it may just affect the tail.  In all expressions, the white hairs on the tail - often in rings or on either side of the tail head - acts as a defining characteristic of rabicano.  It's often called a coon tail or skunk tail.

From Wikipedia.

Rabicano also tends to spread as the horse ages, and unlike true roans, rabicanos won't have corn spots.  It also shows up in breeds (like Arabians) that don't seem to have true roans.

Sabino - and the dominant white patterns I'll talk about in the next post - are just kind of fun.  It's typically notated as sb (off) and either Sb or Sb1 (on).

Sabino is actually a group of patterns.  The one identified for testing is Sabino-1, but there are sabino-like patterns in draft horses and Arabians that behave similarly but test negative for Sabino-1.

On a horse with sabino, you'll see: roaning at the edge of white areas, which tend to have jagged edges; belly spots; irregular face markings (especially blazes) that may extend past the eyes or chin; two or more white leg markings that typically extend above the knees and hocks; and roaning or random white marks ("lacy" or "splashed" in appearance) on the belly, barrel, and flanks.  Unlike splash, there is no link to deafness.

Sabino is another one that can easily be mistaken for something else - or nothing at all.  The most minimal expressions may just be a chin or lower lip spot; on the other end of things, sabino can and does produce pure white horses (and these are healthy, unlike the pure white frame horses).  I've classed it with roan and rabicano because it does have that characteristic roaning to it.

Sabino-1 is known to be incompletely dominant, like cream.  One copy of the gene turned on produces a horse with the typical sabino markings.

Borrowed from Wikipedia.

Two copies of Sb1 produces a horse that is at least 90% white at birth, with the corresponding pink skin under the white pattern.  This is sometimes referred to as sabino-white, especially when the horse is almost entirely white.

I could argue this guy as homozygous sabino or as sabino/splash.  (From a local show)

"Draft-type sabino" typically shows up in Clydesdales, Shires, and breeds related to those two (like Gypsies).  They actually included examples in the study that identified sabino-1, and none of them tested positive for that version of the gene.  What gene it is, they don't know yet, but it behaves like sabino and is generally assumed to be a sabino pattern.

A draft-type sabino will have white facial markings that range from blazes to bald faces to apron faces, which may wrap around the face and generally have feathery, roaned edges.  If they have white on their forelegs that extends above the knees, it may trail up to the shoulder or back of the leg to the elbow, again with the feathery edges.  White on the back legs, which is common, may extend up the front of the leg to the flank.  Belly spots are also common, especially when the white on the legs extends over the knees.

Very typical Clydesdale with draft-type sabino. From Wikipedia.

Unlike sabino-1, it seems like the draft version is only dominant, not incompletely dominant.  Since Clydesdales and Shires are generally a closed population (they're not registering anything that doesn't have parents of the same breed), there should be about 25% of the population that come out with 90% or more white if the draft-type sabino is incompletely dominant, and they just don't see it.  White Clydesdales and Shires are very rare.

To break down that math, assume you have a foal whose parents are both Sbsb.  Baby has four options for what gene pair it gets: sbsb (both off), Sbsb (one on from dad, one on from mom), sbSb (one off from dad, one on from mom), and SbSb (both on).  Four options, so the chance of any given genetic pair is 25%.  And with sabino-1, they see this: with two Sbsb parents, 25% of babies are solid, 50% are sabino (because Sbsb and sbSb look the same), and 25% are sabino-white.  With draft-type sabino, 25% of babies are solid and 75% are sabino.

Similarly theoretical is sabino in Arabians.  Arabians actually have a couple of dominant white patterns, but they also have white with roaning that isn't explained by those patterns; I'll go into this on the dominant white post, but dominant white is for the most part tied to bloodlines.  If a horse doesn't descend from the founder (assuming they've figured out who it was), it's unlikely that they've got the same pattern.  It's always possible that the horses showing sabino could end up being additional dominant white patterns, but for now they're classed as sabino.  As with the draft-type sabino, there's no genetic test for it yet.

As with other types of sabino, you'll see the face white, belly spots, high whites, and roaning around the spots.  The maximum expression in Arabian sabino seems to be about 50% white instead of 90%, and the few apparently sabino-white Arabians have tested negative for sabino-1.  It's not clear at this point if it's a dominant or incompletely dominant gene, as far as I can tell.

So going back to our theoretical horse, who at this point is a smokey grullo with splash, let's assume he also has sabino.  That makes him:

Ee aa CrC zz DD chch toto oo SW1sw Sb1sb lplp

It also makes him a flashy, flashy critter. lol Visually, the splash and sabino look pretty similar unless you look closely, but there's a decent chance you'd be staring at a grey horse with a black mane and tail, a dark stripe down his spine, some seriously high white stockings, an apron or bald face that wraps down onto the lip and chin (or even all the way around the face), and a jagged belly spot.  Maybe a random neck spot or two.

Next will be dominant white, which I love looking into.  I may have to split it up into multiple posts, though - there are over 20 different identified versions of it!  We'll see how much information I dig up.  :)