Conference noted::equitation

    Size is indeed a genetic trait however, not one that is particularly
    predictable.  I can give you some general observations from my
    experience breeding Arabians.  Size charactoristics are generally
    dictated from the Dam line.  This only is true when looking at large
    numbers of breedings for example if you measure the foals of 100
    crosses you are likely to find that the foals reflect the size of
    the Dam, Granddam, or Greatgranddam on the average.  There are many
    other factors however that are involved besides genetics, like the
    number of foals a mare has had (first foals are almost always small),
    the environment that the foal grows up in, the feed, and etc.  Note
    that this also is only true when looking at large numbers of foals.
    The bottom line is that breeding for size or performance
    charactoristics for an individual breeding is like betting on the
    weather in New England.  In the summer you know it should be warm
    but there's always the chance of snow in July.  I will say that
    I have rarely seen a foal who is more than two inches over its dam.
    Given that you are looking for six inches I wouldn't bet on it even
    if she were bred to a shire!  As far as color goes, I think black
    is recessive but don't know for sure.  Since this is a part bred,
    you may be lucky and get black but beware, there are very, very,
    very few black Arabians, and even fewer yet that are worth looking
    at.  Before anyone gets upset and says " Well my friend has a ..."
    I am only speaking in general terms.  This business is all about
    playing the odds and the odds say that this unborn foal will be
    a 14.2 hand bay.  Any takers?
    
    
    Smile,  There's got to be a filly in there somewhere!
    
    Bob
    

    Genetically for size, this foal could end up being just about anything.
    You'll have a MUCH better idea after it is born when you can evaluate
    the length of its cannon bones.  I have seen ALL sizes resulting
    from this type of cross.  It just depends on what the foal has
    inherited.  I have a 16'3" hand mare which resulted from a 15'3"
    hand Arabian stallion and 15'3" hand Thoroughbred mare.  She has
    several full brothers and sisters ranging from 15'2" to 16'3" mature
    height.  She was probably a result of heterosis or hybrid vigor
    depending on where you studied.
    
    Color wise--it depends on whether the black stallion is really a
    black (not a very dark seal brown).  IF the stallion is homozygous
    for black, i.e., BB, then the foal will be black.  Homozygous black
    is rare.  If the stallion has EVER sired anything that wasn't black,
    he is not homozygous black, but heterozygous black or Bb -- extremely
    simplified.
    
    This is really simplified (the only way I can understand it!). 
    Say the mare is bay (bb) and the stallion is black:
                    sire                                  sire
         B    B   (homozygous)         or      B     b  (heterozygous)
                                                 
     b   Bb   Bb     foal would be         b  Bb    bb   foal has 50%
     b   Bb   Bb    heterozygous black     b  Bb    bb   chance to be
   (mare)                                                bay or black
                                                       
    Now that I have bored everyone silly (I studied genetics in school)
    I hope this answers some of your questions.
    

    I was writing my note while Mr. Nickerson was writing his.  I have to
    second his statements about size.  It is hard to predict.  (Plus some
    of us can be really confused when it comes to measuring horses--there
    seems to be quite a few horses around who apparently have been measured
    from the wrong end of the stick.  "You advertised this horse to
    be HOW tall?" 

    The women said that the horse should mature to 15.3.
    she said that the mare has been bred like 3 times.  can you tell
    how big the foal will be when it is born, by how tall it is?

    There are several "tests" for determining how big a foal will grow
    but the only one I've seen that is close is the Cal Poly test. 
    Unfortunately it is done on the foals first birthday (the real one
    not the jockey club one).  You measure the yearling and add four
    inches for a filly and five inches for a colt and that will be the
    mature height plus or minus an inch.  I've heard of other ones which
    measure the length of the cannon bone but I don't know the specifics.
    If the mare has foaled before, maybe you can get a look at the three
    previous siblings and size them up.  Be sure you ask for who they
    were bred to and what the stallion's height was.  Even after you
    see the foal, you'll be taking a chance because the rules don't
    always work.  The safest way to get a 15.3 hand horse is buy one
    that size.  If this woman is so sure that the foal will grow to
    that size, maybe you can work out a contract that calls for a
    measurement at one year.  If the foal isn't as big as she predicts,
    you get your money back and she gets her horse back.
    
    Bob
    

    An old trainer of mine claims that you can measure from the "hole" in
    the front of the knee straight down (no bend in the tape measure) to
    the coronet band and get an estimate.  If that measurement is 15
    inches, the horse will be 15 hands.  If is 14 3/4 inches it should be
    14.3.  We did measure a bunch of horses one night and they were all
    within an inch or so of the estimate.  I have doubts as to how well
    that would work with a tiny baby.          
    
    I've had too many unpleasant surprises with mature heights (speaking as
    an owner of a home-bred 13.3 hand mare out of a 14.3 hand stallion and
    14.3 hand mare--and I KNOW there was no problem with nutrition).  The
    only way I gamble on height is if I already own the foal and/or if I
    don't care what the mature height will be. 

    I agree with Bob Nickerson.  In my (limited) experience raising
    Arabians, the dam has really determined the size of the foal.  This
    year's foal by a maiden mare, though, surprised us all; the foal
    was huge.  At 5 weeeks, his poll came just under my chin (I'm 5'3").
    Th mare is just under 15 hands; the stallion is 15 hands.  Th sam
    stallion produced a colt that is 14:3 hands at 2 years out of a
    14:2 mare.  A second stallion that is 15 h produced a filly out
    of the 14:2 h mare that is 13:2h at one year.  According to the
    Cal Poly test, that filly should reach 14:2 at maturity.
    
    Whether the black stallion has sired any chestnuts will let you
    know that there's a chance the foal could be chestnut, as that color
    is dominant over bay.  Otherwise, the chart Ms. Hoepner provided
    is a good guideline.
    
    THE HORSE by Evans et al goes into genetics in an easy-to-understand
    but complete manner.
    
    Merrie

    RE: 251.7
    
    I'm not sure that chestnut is dominant over bay...
    
    I saw a foal last year by a "dark bay or brown" stallion out of
    a mare of the same color, and it was a chestnut.  Of course, there
    are different shades of bay (these horses were both definitely
    not entirely black, but did have black legs, mane, tail).  If chestnut
    is dominant, this combination could not have produced a chestnut.
    
    I also know of a chestnut mare who was bred twice to a chestnut
    stallion and both times produced chestnut foals; this does not prove
    that chestnut is recessive, but indicates that it could be.  This
    same mare (I now own her) is in foal to the dark bay stallion
    mentioned above, and I am hoping for a dark bay... so I sure hope
    chestnut is recessive.  If it is recessive, I have a 50% chance
    of dark bay, 50% of chestnut (I think).  If it is dominant, I've
    got 0% chance of dark bay.  This is the simplified version; in
    actuality, there is more than one gene that affects color, which
    is how you end up with liver chestnuts, etc.

    Sorry for not including chestnuts in the probabilities for color.
    I'll continue to scrape the egg off my face.  (How could I forget
    chestnuts?--thats my favorite color--besides that it matches my
    hair.)
    
    Chestnut is a double recessive. 

    .9 is correct, chestnut is a double recessive, therefore a chestnut
    bred to a chestnut will always produce a chestnut (unless of course
    someone hopped over the fence for a little quick fun).  I've never
    seen or heard of this rule being proved wrong.
    
    BTW the hole in the knee test sounds interesting, I think I'll try
    it a few times.
    
    Bob
    

    RE: 251.9
    
    That's ok, Mary Jo, no need to scrape egg off your face!  I don't
    think anyone expected a complete genetics manual.  In some magazine
    within the past 12 months (possibly Equus) there was an article
    on color, and it had a complete table of all sorts of colors.  Wish
    I could remember where I saw it.  I was glad to see chestnut confirmed
    as a recessive - not that it is not a nice color!  I like it quite
    a bit, and if my foal is chestnut, that's just fine.  I just also
    like those "midnight bays" quite a bit.  But color is not my biggest
    concern anyway.

    Phew!!!
    
    I'm just glad no one asked about the genetics of palominos (or
    duns).  Thats enough to make you go screaming into the night.
    
    If you find that article, please let us know where to find it. 
    It sounds interesting.  There is not much documentation on horse
    color genetics (RTDM).
    

    I bred my bay mare to a chestnut stallion and got a chestnut filly.
     Every mare booked to that stallion (a variety of colors) got chestnut.
     That's why I assumed that chestnut was dominant.  Sorry for the
    confusion!!!!!
    
    Double recessive, huh?  Both parents of the bay mare were grey;
    the sire of the chestnut stallion was chestnut, the mare was grey.
    The grandsire of the bay mare was grey; I don't know about the color
    of the others.
    
    Again, I should have checked THE HORSE by Evans et al before writing.
     Incidentally, it covers genetice, including color and lethals,
    very well.
    Merrie

    A recent issue of EQUUS covered colors and some genetics.  If you
    look in the index that is published yearly, it should tell you what
    other issues covered colors.  Is it also true then that gray is
    recessive?  Most of the foals I've seen out of gray horses
    were either chestnut or bay, and either one parent or both parents 
    were gray.
    
    If I were to buy the foal in utero, I would not bet that it would
    mature to 15.3, unless I had some sort of guarantee like the one
    mentioned earlier.  You might also consider that the sex of the
    foal could be a factor in the size, since in general fillys tend
    to be shorter than colts.  I know that most of the foals (warmbloods)
    born where I board have proved this to be true.

    RE: 251.14
    
    I think gray is dominant.  That is why you will hear that in order
    for a horse to be gray, at least one of its parents must be gray.
    However, a gray horse may also be carrying a recessive gene for
    bay or chestnut; so, two gray horses could produce a bay (or chestnut),
    but it would be more likely that they would produce a gray.  A
    homozygous gray (double gray gene) theoretically would always produce
    gray offspring, regardless of the other parent's color.
    
    To tell the truth, for years I assumed gray was recessive, because
    you don't see that many gray Thoroughbreds and in fact that color
    often seems to bring a premium...
    
    Gray seems to be more dominant in Arabs, but I can't believe the
    gene would be dominant in Arabs and recessive in Thoroughbreds.
    We're talking different breeds, not species (I was a biology major).
    
    About buying a foal in utero - we're talking big-time risk here,
    so I would be reluctant to spend much money.  The only way I would
    feel that the risk was somewhat minimized would be to deal with
    an established breeder who had a high precentage of "proven" horses.
    The least risky way is to buy a "proven" horse, but of course that
    will cost you more...
   
    

    When I bought my mare (just after she was weaned), I had hoped she'd
    mature to the size of her dam (16hh).  However, she did mature to
    15.1 which is more than the vet at the time predicted.  He (Dr.
    Magee in Marlboro) predicted she'd not get any taller than 14hh.
    
    Not knowing who the sire of my mare was, I had only the size of
    the mare to go on.  We do feel, however, that the stallion was either
    pure or part-Arab.  The Dam was more Thoroughbred/Quarterhorse
    breeding.
    
    My mare was fully mature at age 4 which is when the "holes in the
    knees" closed up indicating she could now handle the weight of a
    rider and tack.  One of the reasons many Thoroughbreds from the
    track have so many problems with their legs is that they are started
    under saddle too young (2 years).  However, that's another story.
    
    

    Gee Mary Jo, I'd hate to make you scream but I've got this little
    dun mare and ..... liesl
    

    I have some questions on color genetics, if anyone is still looking at
    this note.
    
    We had a seal point bay mare.  she was bred to a chestnut stallion and
    birthed a seal point bay colt.  She was bred to the same stallion on
    her foal heat.  This produced a cheastnut with black mane and silver
    tail.  She wasn't bred back to that stallion but has produced only seal 
    point bays since then.  I think she has had 4 more.  What I wan't to
    know is..... why did she throw that chestnut and why were the mane and
    tail different.
    
    	On another note.....I know a mare that threw only line backed
    dunns.  no matter what she was bred to.  Even her offspring are
    throwing lined backed dunns.  Does that mean dunns are dominant???
    
    virginia

    I don't recall the inheritance patterns of dun offhand or whether dun is 
    dominant over chestnut. Chestnut is recessive to most colors.
    
    Your observations also tell me that your bay mare was carrying a chestnut 
    gene. Bay is dominant over chestnut so she looked bay. She could not have 
    produced a chestnut foal otherwise as the chestnut color requires 2 
    chestnut genes to make the horse be a chestnut color. A single chestnut 
    gene can AFFECT the color of the foal(e.g. cremello crossed w/chestnut
    having flaxen mane/tail ALWAYS produces palomino) but a foal w just one
    chestnut gene CANNOT be chestnut.
    
    The fact that the mare produced about 4 more bays with her markings
    could be a simple "lucky" streak with varying probabilities of
    occurrence depending on what she was bred to. For example, the odds are
    15 to 1(6.25%) that she would produce 4 bays in a row when bred to a 
    chestnut stallion. If the stallion were a bay which also carried a
    chestnut gene, the probability rises to 31.6% success rate. However, if
    she were bred to a bay stallion with only the bay genes, she would
    NEVER produce anything but bay foals. The foal would inherit a bay gene 
    from the sire and regardless of whether it got a bay or chestnut gene
    from the dam, it would be bay.
    
    You don't say what color mane/tail the chestnut stallion had but, if he
    had a flaxen(silver) mane/tail, the foal could have inherited a mixed
    bag of genetic modifiers for mane/tail coloring.
    
    I'll look up the dun pattern if you're really interested.
    
    John

    Virginia,
    
    Since you asked about duns, I figure I'd better post this before you go 
    off to Idaho! I looked up the genetics of the dun color. Basically,
    whether or not a horse is dun depends on a genetic dilution factor.
    
    The short answer is yes, dun is dominant but dun horses can produce
    other color foals unless they have 2 "dun" genes.
    
    Actually, there are supposed to be 2 dilution factors in horses. One
               r
    is called c which controls dilution of only red pigment in the hair and
    lightens the color of the mane & tail. The other is called D and dilutes 
    BOTH red and black/brown pigment. When pigment is diluted, it colors 
    only one side of a hair which changes the way it reflects light and 
    that's why the color looks different. 
    
         r
    The c  is recessive and does not affect the coat color of
    black/brown/liver colored horses. It turns chestnuts into palominos and 
    bays into buckskins. If a horse gets a double dose of this gene, a
    chestnut would become a cremello(creamy off white w/lighter mane &
    tail) and a bay becomes a perlino(a buttermilk white with a mane & tail
    darker than the body). It is also believed that this gene can produce 
    red(claybank) duns from chestnut horses.
    
    The D is dominant and has a recessive called d which allows the pigment
    to color the entire hair.
    
    The D factor is what creates most dun colors as well as grulla, etc.
    Since genes come in pairs, a dun may have one or two D factors. If the
    second gene is a recessive d factor, such a mare would throw some
    colors other than dun. If she had 2 D factors, all her foals would be
    some shade of dun. For example, a chestnut bred to a dun could produce
    a yellow dun with matching mane & tail.
    
    You can't tell whether a horse has 1 or 2 D factors by looking at it
    because the second one doesn't change the coat color. But, a livestock 
    breeding book I have at home says that if ya bred a dun mare
    to a stud that was not dun 5 different times and get only dun
    foals, there is a 90% chance that she has 2 D factors. You have to 
    breed to a different color stud so you can eliminate the possibility 
    that his genes made the foal dun. 
    
    So, if that mare you mentioned had at least 5 foals by other color
    studs she was probably doubled on the D factor. If she had fewer foals
    or was bred to another dun, she might have had only 1 D factor and been 
    on a lucky streak. 
                                                    r
    Just to make things even more complicated, the c gene can change the
    shade of a dun making it even lighter than it would be ordinarily. So,
    a dun could throw a palomino when bred to a chestnut!
    
    Does that help?
    John

    Just in case anybody wants to get REALLY into the color genetics
    without buying a new book, here's a summary that I found on usenet.
    
Article: 10504 of rec.equestrian
From: [email protected] (Tracy Scheinkman)
Newsgroups: rec.equestrian
Date: 23 Dec 92 22:33:26 GMT
Sender: [email protected]
Organization: University of Arizona, Tucson, AZ
Lines: 267


	What follows is the article on horse color that I posted last
year, with a few sections updated.
	
	When my mare was pregnant I became very interested in 
color genetics in horses I wanted to know the probabilities for the 
color of the foal.  My mare is a grey, the sire is a bay (our baby is a 
beautiful bay filly rapidly going grey).  This is a basic version of
what I found out.  Some of the terms are a bit technical but I will try 
and make them understandable.

	First, color inheritance in horses is NOT governed by a single gene.
Hair color of horses like hair color of humans and other mammals is governed
by many genes interacting with each other.  
	To a certain extent it can be thought of as a series of transparent 
overlays with a figure of a horse underneath, what color the horse is 
depends on which overlay is uppermost and how much of the underlying colors 
it allows to show through.  For example in the case of a horse which has
both a gene for roan R and a gene for grey G, both of which are dominant
genes, you will not be able to tell that the horse has a roan gene because
the greying covers it up.  The only hint you would have would be when the
foal is just born if their coat is about half white hairs mixed evenly with
the backround color, except at the head where roans do not have as many
white hairs as greys, then you would know that the foal carried roan coloring
but shortly thereafter the foal's coat would begin to grey out as the grey
gene is a progressive whitener of the coat.  Thus as an adult the horse could
conceivably carry a roan gene and yet look perfectly white.
	Now on to the next lesson.  Genes always come in pairs.  Geneticists
label them with a capital letter if the gene is dominant or a small letter
if recessive thus G represents grey color and is dominant, g represents non-
grey and is recessive.  In order to see a recessive color both genes in a
pair must be recessive thus a bay horse would have gg at the grey gene 
location (called a locus) and a grey horse would either be GG or Gg.  Got it?
	Next, not all books use the same lettering system for different
genes a gene called A in one book might be B in another.  Just look for
consistency within the book or article itself.  The book I will be referring
to is called Horse Color and was written by D. Phillip Sponenberg,Phd.,DVM and
Bonnie V. Beaver, DVM.  Sponenberg is a researcher with a university in 
Virginia, I believe, and is still doing research into horse color.  This is a 
wonderfully complete book which includes over a hundred color photographs 
of the various coat colors and patterns they discuss.  The appaloosa 
information which is in the book is incorrect and Sponenberg has recently
published new information on appaloosa inheritance which I have tried to 
include here (see Equus, April 1990 issue).

	Horses have the possibility of two different color pigments, eumelanin,
which is responsible for black and chocolate brown horses and the black in a
bay's mane and tail, and phaeomelanin, which is responsible for the red or
yellow color of sorrels, chestnuts, palominos, and the red body on clear
bays.  Now we're ready for the genes themselves.
	A	a dominant gene is responsible for bay horses by restricting
		eumelanin to the points meaning the mane, tail, and legs of the
		horse, the rest of the horse has red, phaeomelanin, pigment
		(note the exception: dark mahogany bays and seal browns
		have other genetic elements at work, mahogany bays have an
		additional gene allowing some eumelanin, seal browns are
		actually genetically black with another gene P causing 
		light areas on muzzle and flanks)
	a	this recessive gene is responsible for black and uniform
		chocolate brown horses, a common color for Morgans and
		some Quarter Horses, this gene allows eumelanin over the
		whole horse uniformly (as compared with A which restricts
		eumelanin to the points)
	B	this gene is for the black variety of eumelanin
	b	this recessive gene is for the brown variety of eumelanin, the
		difference apparently is in the microscopic arrangement
		of pigment molecules, these horses also tend to have
		amber or light brown eyes and pinkish brown skin, in order
		to have a uniform chocolate brown horse then the horse must
		be aabb, if it is A-bb then it is a bay with brown points
		instead of black points(red body, brown mane tail and legs)
		this gene is only a factor in a few breeds most notably
		Morgan and Quarter Horse
	C	this gene means that the horse's color is fully expressed,
	 	non-dilute
	 cr
	c  	this recessive gene is the cremello gene it dilutes phaeo-
		melanin markedly, eumelanin a little, it is responsible
		for blue-eyed light cream or white horses that some
		call Albinos (true name is cremello if chestnut is diluted,
		perlino if bay is diluted), however there is no true Albino 
		gene for horses, this gene is also incompletely recessive so 
		when big C and little c-cr are present in one gene pair a horse
		that would otherwise have been chestnut or bay would be
		instead palomino or buckskin respectively.  Fascinating, huh!
	D	a dominant dilution gene is responsible for all dun horses 
		except claybank duns which are mostly c-cr horses, this gene
		dilutes body color but not point color, duns have 
		dorsal stripes, some also have leg striping, black becomes
		grullo when D is present, chestnut becomes red dun, bays
		become line-backed buckskins, other examples of dun colors are 
		lilac dun, olive grullo, line-backed palomino, zebra dun, 
		yellow dun, etc. the dun gene D can act in concert with 
		other dilution genes, for example with Cc-cr in the case of 
		a chestnut D- would produce a line-backed palomino
	d	non-dun
	E	this dominant gene allows eumelanin at the points meaning
		it allows bay and black this allowance of black color
		becomes important because of the next gene
	e	this recessive gene causes phaeomelanin red or yellow
		over the WHOLE body and points of the horse in other words 
		chestnut, sorrel, or palomino, this gene is said to be 
		epistatic to the A locus this means that if two e genes are 
		present they cover up the effects of A or a, think of it as 
		opaque plastic overlays the horse might have been black, bay, 
		or chocolate brown according to its other genes but because of 
		ee it's red (note: sorrel and chestnut both generally refer to 
		the same color genetically, red, however different breed 
		associations refer to the lighter phases of the color 
		differently than the darker phases of the color, to further 
		complicate things different breed associations do not agree as 
		to what term shall cover what shade of color)
	 d
	E 	the proof for this gene is incomplete, this is a dominant
		gene at the E locus that causes the color called jet black
		which is a non-sun-fading black color mostly seen on
		Clydesdales and a very few other large breeds it is not
		present for example in Arabians whose black color when
		present comes solely from the normal recessive mechanism
	F	normal red mane and tail on ee, chestnut or sorrel horses
	f	flaxen mane and tail on chestnut or sorrel horses
	G	grey, this dominant gene is like a transparent plastic
		overlay, when the foal is born whatever color it would
		have been without the G shows through, thus it is black,
		or chestnut or bay or whatever, then as it grows older
		it progressively whitens as each new coat gets more and
		more white hairs mixed into it
	g	non-grey
	P	pangare (pronounced pan-gar-ray), this causes light areas
		on muzzle, over eyes, on flanks, stomach, it causes
		black to become seal brown and chestnut with flaxen mane
		to become blond	sorrel
	p	non-pangare
	Sty	smutty, causes some black to become mixed into body coat
		clear sorrel becomes chestnut or liver chestnut, clear bay
		becomes mahogany bay, palomino becomes smutty palomino, etc.
	sty	recessive causes clear pure color, a clear pure red is 
		often called sorrel among Thoroughbreds and Quarter Horses
		other breeds call this chestnut
	Z	silver dapple, causes eumelanin to be diluted to flaxen usually
		a little eumelanin remains in the coat, silver dapple bays are
		possible when the eumelanin in the mane and tail are diluted
		causing the mane and tail to have a silvery color to them
		because of some of the remaining black hairs, this gene is 
		really only a factor for breeds such as Shetlands, Icelandics, 
		Dutch Warmbloods, and Norwegian Fjords, Norwegian Fjords may 
		have a combination of silver dapple and dun genes
	z	non-silver-dapple 
	R	roan, causes white hairs to be mixed with base coat color,
		this color is non-progressive as opposed to grey which
		is a progressive whitener, though it does change a little
		with the seasons, roans often have fewer white hairs mixed in
		to the base coat on the face and legs than on the body, also 
		this gene is thought to be a dominant lethal meaning that RR 
		horses die during development, most roans are Rr and throw 
		solid colored foals as well as roans, Dutch and Brabant draft 
		horses may be an exception to this rule and if so roans in 
		those breeds are probably due to some other mechanism
	r	non-roan
	T	tobiano paint spotting, this paint color has bold sharp edges
		and has white in a vertical pattern that often crosses the spine
		the face and legs are usually dark the amount of white is 
		governed by independent modifiers and can be selected for, 
		thus a tobiano with a lot of white will tend to have foals with
		a lot of white, homozygous tobianos, meaning TT horses, will 
		throw 100% tobiano color
	t	non-tobiano
	O	non-overo
	o	overo paint spotting, also called frame overo, there is some 
		argument over whether this gene is recessive or dominant, the
		color tends to splash in a horizontal pattern with sharp edges
		that rarely crosses the spine, the legs and face are often 
		white, blue eyes are common, overos that are mostly or all 
		white die within a few days of birth because of a malfunction 
		of the colon, there may be another gene at this locus that is 
		responsible for these lethal white overos, the amount of white 
		caused by this recessive gene is governed by an unknown 
		mechanism possibly womb temperature maybe independent genes 
		but cannot be selected for, overos often throw solid or nearly 
		solid foals 
	Sb 	sabino paint spotting, often confused with overo, this may be 
		an example of incomplete dominance such that homozygous horses 
		SbSb have more extreme patterning and markings than 
		heterozygous horses Sbsb, this pattern is typified by extremely
		ragged margins rarely crosses the spine and blue eyes are 
		common, the minimum expression seems to be high white 
		stockings and extreme facial white, this gene is common amongst
		Clydesdales where the color is sometimes erroneously called 
		roan, many sabino horses exhibit the Medicine Hat pattern 
		popular among some breeds such as the North American Spanish, 
		pure white foals develop normally in contrast with overos
	sb	non-sabino
	Note: the term tovero refers to a horse which exhibits a combination
		of overo and tobiano patterning, such horses would be 
		genetically T-oo, a horse that is genetically T-ooSb is 
		theoretically possible, either tovero or sabino horses may
		exhibit the Medicine Hat pattern
	Rb 	rabicano, which is a white hairs starting at the dock of the
		horse's tail and sometimes white hairs mixed in the flank area
	rb	non-rabicano
	W	dominant white, neither this gene nor the c-cr genes are true 
		albino genes as some pigment is still present, the skin of
		dominant white horses is pink, the eyes of such horses are 
		usually brown, this is a dominant lethal gene meaning that all 
		dominant white horses are Ww, the WW form apparently dies in
		development there are no exceptions
	w	non-white
	Apl	non-appaloosa, to be a non-appaloosa the horse must be
		Apl Apl
	apl	this is another incompletely recessive gene, apl apl horses
		are the few spot appaloosas that produce 100% appaloosa
		babies no matter who they are mated to, Apl apl horses are
		the brightly patterned appaloosas we are most familiar with,
		other modifier genes cause the different patterns -- leopard,
		blanket, varnish roan, etc. -- combination patterns are 
		common, for example I once saw a black varnish roan with a 
		white blanket over the rump and leaopard spots over the 
		whole horse, there may be other appaloosa mechanisms that 
		are unknown currently (note: the grey gene has the same affect 
		on appaloosa pattern spots and splashes that it has on solid 
		colored horses and eventually such appaloosas that carry the 
		G grey gene will become completely white just as solid grey 
		horses do, in those cases the skin under the white hairs is 
		often visible and is pink in the blanket areas and dark where 
		the spots or solid areas were, thus an all white horse with 
		pink skin and a few oval spots of dark skin may actually be a 
		few spot appaloosa that has turned grey) currently there are
		about eight different known appaloosa patterns, there may be
		a form of Appaloosa roaning (or greying) which only affects
		the backround color and does not affect the spots however
		evidence for this is not available

	Now how it works, let's take the case of a black horse, which is one
of the most difficult colors to achieve in most breeds.  Remember that
chestnut ee covers up black aa and bay A-.  So a chestnut horse with a black
ancestor is bred to a bay horse with a black ancestor, the chestnut's gene
pattern looks something like a?ee the bay's gene pattern looks something
like AaE?, now there are 16 different combinations possible of which 4 are
definitely bay, 4 are bay or chestnut depending on what genes the ? are,
4 are chestnut or black, 2 are bay or black, and only 2 are definitely black.
If we make the first ?=A and the second ?=e then, the possible offspring
are 8 chestnuts, 6 bays, and 2 blacks in other words a ratio of 4:3:1.   When
you add more color genes it becomes more complicated.
	As to the grey question, grey covers up the base color, let us say
that color is bay, well bay can hide a black gene or a chestnut gene, so
depending on what the grey is bred to you could have a chestnut, a bay, a
black, or another grey, or numerous other colors.  Remember to look at
your horse's breed and parentage, certain breeds don't have some color genes
available to them.  For example Arabians don't have Z silver dapple or E-d
jet black, or b chocolate brown so those genes are unnecessary to consider.  
My mare's line has had nothing but greys, bays, and chestnuts for many 
generations, black may have been known many generations ago but hasn't shown 
up since then so I won't need to bother checking for other colors such as 
overo genes or cremello genes when I breed her to another of her line.  Since 
I am interested in black I would want to see if the sire had a line that 
included black genes.  One more thing, the likelihood of a recessive gene 
showing up in subsequent generations decreases with each new generation that 
does not show it, but, as in the case of black coloring, it never completely 
goes away.  If on the other hand you selectively breed away from a dominant
color it can be completely lost in one generation (that actually happened
with the Crabbet Arabians in the early 1900's, it wasn't until Skowronek
was found and purchased that the grey color reappeared in the Crabbet herd.)

				Tracy 

    thanks, I needed that...

    Yeah, I needed that too.
    
    Thanks again John.  I do have some books on color genetics.  I just
    have to find them now.  As far as the dun mare I talked about, she
    passes away a while back but her last foal (She threw only fillies too)
    has thrown a dun also and is the spitting image of her grandmother. 
    Right down to the face and leg markings.  Kind of spooky if you ask me. 
    The mare was breed to a bay stallion who throws mosty bay foals (colts
    too, this was a filly again).  The whole thing has puzzeled all of us. 
    WE are thinking of calling UNSOLVED MYSTERIES about this one.
    
    virginia