If you breed a dark bay mare to a chestnut stallion what is the propensity of getting a chestnut foal? Sire of mare was chestnut and dam was dark bay. Any color afficianados out there? Which color is dominant?
If I breed this mare to a bay stallion, there are no guarantee the foal will be bay, but isn’t it more likely?
Speaking solely to the three base colours of Bay, chestnut and black: Bay (EE/Ee AA/Aa) is dominant to chestnut (ee AA/Aa/aa), and chesnut is dominant over black (EE/Ee aa).
EE/Ee/ee - red factor
AA/Aa/aa - Agouti and deals with how the black is distributed.
Of course, Grey (GG/Gg) is dominant to all colours (gg).
In your case, the chestnut stallion is ee AA/Aa/aa and the dark bay mare would be Ee AA/Aa.
With that info, the foal would have 50% chestnut, 43.75% Bay and 6.25% Black
Breeding to a bay stallion (EE/Ee AA/Aa) would result in 82.03% Bay, 12.50% Chestnut and 5.47% Black.
http://animalgenetics.us/CCalculator1.asp is a useful tool… The more information that you have, the more accurate the % becomes.
the dark bay mare would be Ee AA/Aa/aa.
…
Breeding to a bay stallion (EE/Ee AA/Aa/aa)
A bay could not be aa- only AA or Aa result in bay horses (EE or Ee with aa would be Black). I think you knew this but just clarifying for other readers 
The website mentioned above is very helpful. Your mare is Heterozygous for black/dark base (She is Ee), which we know for certain because she had a chestnut parent who gave her a “e”. It is unkown whether she is homozygous or heterozygous for Agouti (the gene that turns blacks into bays) so she might be AA or Aa.
Hope this helps.
So,
Does that change anything with regard to the above?
I think people get bamboozled with all the genetics.
Keep it simple, the mare has inherited one chestnut gene from her chestnut sire. So if you breed her to a bay stallion that also has a chestnut parent then you will have a 50% chance of a chestnut foal because he too will have passed on a red gene.
Not going to go into the bay side of things as you haven’t asked for that.
If the stallion you breed her to is homozygous black (no red gene) the mare cannot produce a chestnut foal because black is dominant over red.
So if your aim is to avoid breeding a chestnut foal breed to a homozygous black stallion.
If I breed this mare to a bay stallion, there are no guarantess the foal will be bay, but isn’t it more likely?
No because she could still produce a chestnut foal if the stallion you use carries red.
First question does the stallion you wish to use have a chesnut parent?
[QUOTE=TrinitySporthorses;6171360]
A bay could not be aa- only AA or Aa result in bay horses (EE or Ee with aa would be Black). I think you knew this but just clarifying for other readers
QUOTE]
Thanks TrinityS. too many A/a combo’s and not enough proof reading 
As for the %, my typo doesn’t affect the numbers from animalgenetics.us.
Well, simple only works if it’s accurate… 
If two bay horses each have a chestnut parent, so they each have a black gene and a red gene, then there is only a 25% chance of a chestnut foal. Four options, equal chance of getting each option:
Black gene from both (foal is homozygous black, and either black or bay in phenotype)
Red gene from both (foal is chestnut)
Black from sire, red from dam OR black from dam, red from sire (foal is heterozygous black, and either black or bay in phenotype)
If you breed the EeA? Mare to a bay stallion who is, because we don’t know otherwise, E?A? The. Yes, the odds of a bay foal are greater, based on just what we know, than breeding her to a chestnut stallion
That’s because we KNOW each parent is at least Ee, meaning 75% chance at black-based to start, and each has at least one A.
We don’t KNOW the chestnut stallion is A? Though odds are pretty good he is, again, not knowing anything else.
If the bay mare is EeAA then breeding to chestnut ee?? is 50/50 bay or chestnut.
Breeding to an EeA? stallion is 75/25 bay/chestnut.
If each parent is Aa then divide the bay odds another 75/25 between bay and black, respectively.
[QUOTE=Bascule7;6171297]
If you breed a dark bay mare to a chestnut stallion what is the propensity of getting a chestnut foal? Sire of mare was chestnut and dam was dark bay. Any color afficianados out there? Which color is dominant?
If I breed this mare to a bay stallion, there are no guarantee the foal will be bay, but isn’t it more likely?[/QUOTE]
50% chance of a red foal for the reasons cited above.
Black is dominant
Agouti is also dominant (restricts black to the points in a black-based horse, in other words, bay/dark bay)
Yes Joz was answering question 1 first and mixed it up with OP’s second question. 50% if bay mare bred to chestnut stallion because bay mare carries chestnut. Apologies 
not to distract from the OP, but I have a color question along these lines…
I have a chestnut mare bred to a bay stallion. After reading this I looked at her pedigree to see where the chestnut came from. I am sure it is in here somwhere but I am only seeing bay??
http://www.sporthorse-data.com/d?d=anaconda+g&sex=&color=&dog_breed=any&birthyear=&birthland=
She is bred to a bay stallion who has a chestnut and a black grandsire
http://www.sporthorse-data.com/d?d=baroncelli&sex=&color=&dog_breed=any&birthyear=&birthland=
I was thinking we had a 50/50 chance chestnut or bay. What do you color gurus think?
Well I bred my bay mare( chestnut mom, bay dad) with the agouti gene, guess from her color, to a chestnut twice and got 2 bays. The mare’s first foal was by a more seal brown type bay stallion and I got a chestnut. The only color I refuse to have is grey and that is easily controlled. Other than that I breed for what best suits my mare and hope for healthy. The rest I don’t care about.
Terri
Thanks!
Thanks to all who replied. I have had a horse of every color except mahogany bay. I won’t do grey again because I spent half my life trying to clean him up for the show ring. My chestnut had a horrible time with scratches in the summer no matter what I did. Then again, the bay with the chestnut pappa has had her own problems with them from time to time. Anybody out there with chestnut children who haven’t had a problem with scratches?
Railmom, the fun thing about chestnut is it can hide for MANY generations :).
To be chestnut means 2 copies of e - ee. A horse who is Ee will be black or bay or brown or some variation of that. E is dominant so all Ee horse bred together only have a 25% chance of producing a chestnut.
As to your breeding - the stallion has a brown sire (by chestnut out of ?) and gray dam (by black out of gray) so we still don’t know whether he is EE or Ee, unless someone knows if either 1) he’s been tested or 2) he’s produced a chesnut (which would make him Ee).
Since that’s unknown we don’t know at this point if you have any chance at chestnut. If you do, yes, it’s 50/50
[QUOTE=Bascule7;6171820]
Anybody out there with chestnut children who haven’t had a problem with scratches?[/QUOTE]
Yes.
[QUOTE=JB;6171866]
As to your breeding - the stallion has a brown sire (by chestnut out of ?) and gray dam (by black out of gray) so we still don’t know whether he is EE or Ee, unless someone knows if either 1) he’s been tested or 2) he’s produced a chesnut (which would make him Ee).
Since that’s unknown we don’t know at this point if you have any chance at chestnut. If you do, yes, it’s 50/50[/QUOTE]
Thanks! I found chestnut offspring from this stallion, so I guess I am back to 50/50
[QUOTE=Bascule7;6171820]
Thanks to all who replied. I have had a horse of every color except mahogany bay. I won’t do grey again because I spent half my life trying to clean him up for the show ring. My chestnut had a horrible time with scratches in the summer no matter what I did. Then again, the bay with the chestnut pappa has had her own problems with them from time to time. Anybody out there with chestnut children who haven’t had a problem with scratches?[/QUOTE]
Scratches, aka mud fever, have nothing to do with horse color although people swear white ankles get them more then any other color, but I’ve seen it on every single color of horse from black to chestnut to grey to palomino to pink, purple and orange. Dark pasterns, white, or chestnut pasterns, doesn’t matter, it’s been seen on all of them.
I feel for you though. It’s a tough bugger to get rid of unless you have a naturally dry environment. We’re lucky where we live, knock on wood…we don’t have it on our farm and I’m pretty sure it’s because it’s so extremely dry. I only have one mare who has it, but she arrived with it on her hind pasterns, but it’s drying up by itself without treatment because it’s been so crazy dry all winter.
Here’s a fun color calculator:
http://www.animalgenetics.us/CCalculator1.asp
You put in the sire and dam color and it will tell you the likelihood of the foal’s color.
Want my opinion on scratches? Make sure that’s actually what they are. It seems I spend my time and energy eradicated buttercups because it’s not the mud that’s doing the damage. It’s photosensitivity. And more often than not it’s buttercups doing the damage. If it was just plain ole mud then every horse I owned should have it. The chestnut does not. The mare has a smidgeon as does her bay daughter. She never had any in 5 years of life until she was turned out when away last year. I then brought her home. Now I suspect she will always be quite sensitive. It’s coming from inside not outside forces.
Terri
It IS true that pink skin is more susceptible to scratches/mud fever/dew poisoning but that doesn’t mean black skin (it’s not about hair color) can’t get it too.
It can be buttercups (which can really do a number on muzzles too, but that’s not the same issue as actual scratches), it can be clover, it can be sunlight combined with dampness, it can be mud, there are several instigating factors.
Most healthy horses just don’t get these skin conditions when it’s a bacteria/fungal thing (buttercups are a whole 'nother story), as the immune system is quite capable of dealing with it.
So, if you have a horse or a barn with chronic issues, look at the dietary management - copper and zinc in particular can be too low and that’s your only sign
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