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Ammit · Feb 5, 2026 9:32 PM

Why is white factor going away?
WF has been part of this game for as long as we have had visible markings. It has always represented untestable accumulated mutations that cause white markings to express at higher or lower amounts. These days with 10 known splash variations, 40+ known KIT mutations, and these new HPS5 variants, WF is simply no longer needed. Those once mysterious genetic factors are now known.

What will the new system be?
There are three known versions of HPS5 so far. That makes things really straight forward when it comes to converting WF to inherited HPS5. The WF amount a horse has will just be swapped for an equivalent HPS5 combo.

The three versions of HPS5 that have been found are EW1, EW2, and EW3. To make this transition easy I am going to be making EW1 worth 1 point of WF. EW2 is going to be worth 2 points, and EW3 will be worth 3 points.

To be clear, that is not how these genes work in real life. There is no evidence EW3 is louder than EW1 but in the name of making something playable as a game that is how it will be handled.

How will your horses change?
What genes your horse receives will be based on the white factor they currently have. They will be assigned one of the genetic combinations listed for their WF. This will not follow pedigrees. If your horse is WF none but has two WF extensive parents the game won't check for that.

None: -/- [0 points]
Minimal: EW1/- [1 point]
Light: EW2/- or EW1/EW1 [2 points]
Medium: EW2/EW1 or EW3/- [3 points]
Large EW2/EW2 or EW3/EW1 [4 points]
Extensive: EW3/EW2 or EW3/EW3 [5+ points]

How will this be inherited?
Once WF becomes HPS5 it will inherit like any other gene. While any horse created before the switch will have HPS5 alleles assigned based on the WF they had, all breeding that happens after the switch will only inherit HPS5 alleles from their parents. Like any other gene you only be able to access the alleles the parent horse has in the GMT lab.

What's the timeline?
This won't be a particularly complicated update, but I am also not in a rush to get this one out. When I have a free day or two of work time I will squeeze this in. Expect this some point in the coming weeks.

The company that discovered these is notating them as EDXW#. To make things a bit cleaner for the game will be using EW# instead.

kitinaround · Feb 6, 2026 2:40 AM

Actually I think I will like the system better it's always been kind of difficult for me to figure out whether or not a horse is going to inherit too much of a white Factor for my program as you can breed two horses one time and it come out fine and then the next time it come out excessive or lethal I think this will be hopeful at least for me as I'll be able to see the factors that could possibly go into the horse genetics for that pairing and I'm honestly looking forward to this

silverborn · Feb 6, 2026 5:34 AM

This is neat!

I might have misread the article, but it looked like the EDXW1 gene restricted white from covering the body beyond a certain point, in one example. (The horse had w20 and tobiano and edxw1 and was barely marked)

Is it going to have a similar effect in game? Like if you got W1 on an edw1/edw1 it would be almost solid colored?

Ammit · Feb 6, 2026 7:18 AM

I did not see anything to suggest that EDXW1 restricts color. Would you mind seeing if you can find what you are talking about?

ETA: I checked the research paper again and there posts for as far back as could but I don't see anything like that.

This horse is w20 and EDXW1 and very loudly marked.

https://www.facebook.com/photo.php?fbid=934175978711298&set=pb.100063567129507.-2207520000&type=3

silverborn · Feb 6, 2026 5:12 PM

I just found the eden white paper again, and I think I was mis-remembering. It's probably from one of the other papers I had found with one of the dominant-white mutations. Please disregard :-??
I remember the one I had been looking at and marveling at, there was a horse that had Wsomething with tobiano and W20 but was barely marked. So it may have been W22 or 34 or 35. Either way, not related to this gene.

VenemousGiant · Feb 25, 2026 6:05 AM

This is so cool! I’m excited

Ammit · Mar 22, 2026 9:30 PM

Update!

I have started the process of rolling this out. You will see the HPS5 gene start appearing today but I am unsure if HPS5 will start influencing image generation today or not. It will be soon if not today.

I decided to go with WF1, WF2 and WF3 as hypothetical alleles instead of using the the real EDXW# alleles. We will add those in eventually but I am more comfortable waiting to use the names of real genes until they can be implemented realistically.

Ammit · Mar 22, 2026 11:15 PM

Every horse has been assigned HPS5 based solely on their white factor. This intentionally ignores pedigree information. HPS5 WF genes can now be created, inherited and gene modified in the lab. They are not currently impacting the appearance of the horse. I expect that to be out on Tuesday or Wednesday. All white factor based herd helpers are currently useless.

Ammit · Mar 24, 2026 12:44 AM

HPS5 White Factor is now fully implemented in the game!

Will my horses change appearance?
If you created or bred a horse in the past 24 hours, it is possible that their new HPS5 White Factor amount does not match the WF they had before. This might result in the amount of visible white changing. Or if you edited HPS5 in the gene lab in anticipation of this update, you may also see visible white changing. No other horses in the game will change in any way.

The way WF is shown in the game has not changed at all. Only the way it has inherited has changed.

How has inheritance changed?
Before WF was semi-inheritable with a random factor. Now it inherits like any other gene. Two HPS5 -/- (formerly wf none) horses will only produce HPS5 -/- foals. If you want to keep overall white factor down that is easy to do by simply sticking to the lower WF values.

How is lethality impacted?
From the updated Gene Guide listing about HPS5:

In HorseGeneticsGame.com HPS5 alleles are never directly lethal in any combination. In some combinations of KIT mutations, and some combinations of splash mutations HPS5 status may be enough to push a foal into the excessive white range causing it not to survive. When pursuing high white crosses, with high risk, sticking to HPS5 -/- can reduce negative outcomes.

And from the change log today:

The old wf has been removed from the breeding algorithm and will no longer have any impact on lethality. The new HPS5 White Factor is now in place and serving the same role instead. Keep your HPS5 factor as low as possible, ideally -/- to limit the chances of lethal foals from genetic crosses that are only sometimes lethal. Reminder that frame, splash and KP also contribute to your odds of an excessive white foal even with KIT crosses.

- is 0 points of white boosting
WF1 is 1 point of white boosting.
WF2 is 2 points of white boosting.
WF3 is 3 points of white boosting.

So -/- gives you 0 times the risk and WF3/WF3 gives you 6 extra points of risk.

Please let me know if you have any questions.

silverborn · Apr 2, 2026 4:20 PM

SB G1 Configure in the Sky

This horse is only showing the HPS alleles on her secondary strand. I regenerated and that didn't change. If I click "show all" it is null/null.

Is there going to be a way to force that one to show up without showing every single locus in the testing window?

Ammit · Apr 2, 2026 8:57 PM

Everything looks correct for her. -/- Is a perfectly valid form of this gene.

silverborn · Apr 2, 2026 9:06 PM

Yes, I just meant since it always showed the white factor at the bottom before, if the genes were going to be null if there's a way to make that show up.

The old way, if white factor was none, it still listed the absence of white factor.

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