Coat Genetics?

[wildwoodstables]

Hey guys! Just wondering if the genetics for coat colours are fairly realistic? ( ex. Ee / aa = black , EE / Aa = Bay ) or if you breed a bay roan to a red roan ( who are both heterozygous roan ) that there would be a chance that the foal be homozygous? I have tried implementing the genetics into my breeding and they seem fairly realistic with patterns and dilutes ( cream, champagne, etc ) but the coat colours ( aa and ee ) seem a bit off sometimes. Thanks

[Nazarach]

Hey guys! Just wondering if the genetics for coat colours are fairly realistic? ( ex. Ee / aa = black , EE / Aa = Bay ) or if you breed a bay roan to a red roan ( who are both heterozygous roan ) that there would be a chance that the foal be homozygous? I have tried implementing the genetics into my breeding and they seem fairly realistic with patterns and dilutes ( cream, champagne, etc ) but the coat colours ( aa and ee ) seem a bit off sometimes. Thanks

Hi there ^^
Normally it should work like this (so, percentage based). Though what exactly do you mean when mentioning aa (non agouti/black) and ee (non-extension/red) seeming off?

Best color/coat guide is in this topic:
viewtopic.php?f=13&t=2158

[wildwoodstables]

Hi there ^^
Normally it should work like this (so, percentage based). Though what exactly do you mean when mentioning aa (non agouti/black) and ee (non-extension/red) seeming off?

Best color/coat guide is in this topic:
viewtopic.php?f=13&t=2158[/quote]


I have had horses ( deceased now or sold ) that should have been EE through parentage ( completely black and blue roan parentage and grandparents ) and have produced a red foal which shouldn't be possible as a EE can only produce a black or bay based offspring...so im just going to presume that I had something marked down incorrectly haha

[Howl]

The genetics seem correct for base colours except there is At in this game “brown” which was disproved in real life genetics. So while that does mess up some of it the bay red and black are accurate.
Some genetics seem to stack here that do not stack in real life. Also phenotype is not realistic for example there is no visible difference in the double creams in real life but there very much is here.

[Nazarach]

I have had horses ( deceased now or sold ) that should have been EE through parentage ( completely black and blue roan parentage and grandparents ) and have produced a red foal which shouldn't be possible as a EE can only produce a black or bay based offspring...so im just going to presume that I had something marked down incorrectly haha

If the parents were 'merely' black-based (- and even if for a couple generations) the probability of the horses displaying EE is just rather high - BUT if they threw a chestnut, then the parentages (if black) were actually Ee aa.

The foal equally misses any agouti; though they are red-based cause they got the (when both parents have Ee) 1 in 3 probability of lacking Any extension genes (so, chestnut from black-coated parents: ee aa).
if they had inherited even just one, then they indeed would've been black-coated like the parents (so black for [Ee aa] as well as [EE aa]).

always keep in mind that the probability of throwing black from black parents is just rather high - never just go with 100% for EE cause you never might know it until its disproven personally i always mark them E_ - meaning they might have EE but it could go the other way - till they throw a chestnut; then i can obviously peg them down to Ee.

hope this helps a bit

[Silverine]

I have had horses ( deceased now or sold ) that should have been EE through parentage ( completely black and blue roan parentage and grandparents ) and have produced a red foal which shouldn't be possible as a EE can only produce a black or bay based offspring...so im just going to presume that I had something marked down incorrectly haha

HWO is as close to life as is possible for horse coat color genetics. Yes, a horse that is EE can only have E- offspring. But not every black-based horse is EE. Even a horse that has all black-based ancestors as far back as the AC could be hiding an e. We have no way to know for sure because we do not yet have genetic testing.

For example - I breed my own herd of Knabstruppers specifically for black leopards. It took at least twenty generations before I became even close to relatively certain that I had successfully bred out any recessive extension. Even now, I would be mildly surprised but not shocked if one of my breedings threw a red foal. It hasn't happened in I can't remember how long but without testing there's no way to know with 100% certainty that I don't have little e running around in my herd.

The genetics seem correct for base colours except there is At in this game “brown” which was disproved in real life genetics. So while that does mess up some of it the bay red and black are accurate.

The existence of a brown agouti mutation has not been disproven, it simply has not been proven. And as far as I am aware there is no currently on-going research into the gene. There is actually only one known mutation of the agouti gene - the recessive mutation that causes black pigment to be expressed over a horse's entire body. This deletion causes the protein that normally restricts black pigment to become non-functional. This deletion is also the only part of agouti that we can currently color test for - we check if a horse has 0, 1, or 2 copies of this specific mutation. We do not test for "dominant" agouti because there is no test for it. We label any horse that has 0 copies of the 'a' mutation as AA, a horse that has one as Aa, and a horse that has two as aa to denote how many copies of the known mutant were detected.

This means there can be any number of different alleles under the 'A' moniker. Heck, there could be fifty different variations of A, each coding for different amounts of black expression. It's unlikely, but still technically possible. There is enough anecdotal evidence for many horse people and scientists to believe that there is at least one other mutant in the agouti genotype. HWO uses the model that says there are two mutants - A⁺ for wild bay and A^t for brown. Unfortunately the only way to know how correct or incorrect any of these models is is to actually decode the 'A' allele in order to determine if it is in fact one single allele or multiple different ones that have not yet been discovered.

As an example of this on a different locus - the cream and pearl genes. Cream and pearl are mutations on the SLC45A2 gene. However it was recently discovered that they are not the only possible mutations on this gene. Snowdrop and Sunshine (links are to scholarly articles) were recently discovered as mutations on the same gene. This means that what we denote as "n" (for "normal") on HWO was actually at least three different alleles. Snowdrop and Sunshine were both found to cause a pseudo-homozygous cream phenotype on horses that tested as nCr. Snowdrop was found in the Gypsy Vanner breed while Sunshine was discovered in a Standardbred-TWH cross.

TL;DR
Genetics notation is complicated. 'a' is used to denote one specific mutation while 'A' basically just means "everything else" and does not denote one specific string of genetic code.