# Inbreeding: what about the doe's recessives?



## Seafolly (Mar 13, 2012)

I've always wondered, but now it's extremely relevant to me. I inbreed, breeding daughter back to the same buck. So far so good, now weaning F3. I understand this brings out undesirable recessives. However, would this method bring out the doe's recessives or just the buck?

I am looking at a splashed rex doe that would be quite a hassle to access but would be amazing to bring into Ontario. However, I'm talking to the breeder and she wrote this:

"This litter's great grandma and great great grandma were albino lab mice. They had a genetically predisposed condition called necrotizing dermatitis of the pinna, unique to their strain - the ears rot off as the mice age. Thankfully this is recessive and none of the offspring who were crossed with pet and exotic mouse strains have ever showed signs."

So...obviously it's carried. Is the outcrossing preventing it from showing up? Would I likely run into problems if I continued to breed daughters back to my (healthy) buck using this doe?


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## pro-petz (Nov 14, 2012)

I would have thought you are initially outcrossing so pairing back to the outcross to linebreed would be weakening the recessive fault each time, the problem would arise if you paired up to one of the bucks from future pairings to either mother or sibling.

To overcome this it may be feasible to pair the doe in question with 2 separate bucks and bring the bucks from one with the does from another thus producing your desired features and hopefully diluting the recessive bad trait in the process.


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## Seafolly (Mar 13, 2012)

Hmm, outcrossing is very difficult for me as I really only have access to feeder mice - the stores where I bought the original pair haven't carried more than one litter since (wish I bought more!). Although they sound the same, the feeder mice are quite obviously extremely poor type making my pet store mice look stunning (they're not).

At the moment, my two bucks are related (one fathered/grandfathered/great-grandfathered the second) so I'm guessing that doesn't count?  I do like that solution though, and would likely pursue that option! I recently made a contact with a black satin long haired male. It's possible she'd let me borrow him. He's a feeder type, but he's the only option I can think of short of delving back into Toronto's feeder bins.

It also occurred to me that I will rapidly lose that rex coat without more rex mice...inbreeding would be the only option there. I suppose I could simply view the rex as a lost cause and focus on the splashed...?


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## pro-petz (Nov 14, 2012)

using your existing males all the young they produce mated to your rex will carry so you will still have the gene just a longer route to take to get them. Not that good at genetics so do not know if they are dominant or not.

if you can borrow a male to pair with the doe aswell you can produce a new line for the rex and splashed using the same technique. May not get them in the F1 but breeding the 2 lines of F1 together will produce the results


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## Seafolly (Mar 13, 2012)

Oh I'm really just mostly worried about the ear condition popping up. It'd be pretty sad to bring back a mouse from the States only to have it bring an awful genetic condition to the line. Perhaps borrowing that poorly typed buck, and using him for one litter, then bringing in my own buck might distance it enough...? I'm awful with genetics too.  Rex is dominant, yes, as is splashed I think. This makes my brain hurt.


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## PPVallhunds (Jul 26, 2010)

If it's a simple recessive thing and not a combo of genes then breeding the splashed to bucks of another line will keep the condition hidden as long as you never pair the siblings tougher or back to the mother. So you could inbreeding back to your bucks as much as you want and it won't pop up as long as you never use a buck desended from her.

however as the breeder has been doing that it is possible the splashed doe doesn't carry the gene as it could have been bred out. The only way to figure it out would be to keep a son and breed it to her and see if any ears drop off, if any do you know she has the gene if none do she may not have it, I say may not as if she is a carrier any Baby she produced should have a 50/50 chance of being a carrier, so if the buck you keep doesn't carry but she does none will have it. If you had a buck from her who had the problem you could breed him to the doe s to tell if they have the gene, then only keep the ones who don't have it and then you will know you have bred it out. But I know some would not feel happy with doing that.

So say EF is normal and ef is the ear falling off gene.

So ef/ef ,ears will fall off
EF,ef. Carrier
EF/EF clear.

So at worst the she would be a carrier EF/ef at best clear.
EF/ef put to your buck EF/EF makes
50% EF/EF clear
50% EF/ef carrier

If you bred the offspring at some point and unlucky to pick two carriers 
EF/ef to EF/ef
50% carrier
25% clear
25% ears fall off

So really it's up to you if you would be happy to either keep it hidden and not know who if anyone is carrying it by breeding to your bucks never any bucks produced from her line. Or take a risk every so often and hope for the best by doing the odd inbreeding for colour ext, or test breed to try to work out who are carriers and who are clear. Or ignor it and just in breed and cull any who pop up with it. Those are your four options really if you want to breed her.

This is where in dogs breeders would use genetic testing to work out who is who and breed accordingly.


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## Seafolly (Mar 13, 2012)

This is...fantastic. Thank you SO much for breaking it down! I copied it out onto paper and think I can now make sense of this.  I think the best route will be to use my bucks (sad, as one of her males has an excellent rex coat) and inbreed. This will mean keeping the babies longer than usual but she said the condition popped up between 3-4 months. Not too long a wait. I don't have qualms culling mice who are ill. The only problem I've yet to solve is where to get the next buck (say, next year) but perhaps by then it would have been bred out. Ideally I'd start another line entirely to keep a buck from but I do need to stay small scale (and then I'm back to square one in regards to finding yet another doe). Need to think on this.


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## PPVallhunds (Jul 26, 2010)

Are you still breeding for type? If so you can have two lines your type line then this splashed line and do it like this.

Your buck X splashed doe

Keep back daughters

Your buck X splashed daughters

Keep back 3rd gen daughters

Your buck X 3rd gen daughters

Keep 4th gen daughters

Ect ect

Then when needed or wanted add a buck from your type line

Type buck 1 X 4th gen daughters (or whatever gen your on)

Keep daughters

Type buck 1 X daughters

Keep gen 2 daughters

Ext ext

Then type buck 2 X whatever gen your on


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## PPVallhunds (Jul 26, 2010)

Doing the above you will never get mice effected with the condition as your mice should not carry it, but you won't know if any of your does carry it or not. also don't ever add the splashed line into the type line as if you did you could introduce that condition into them.


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## Seafolly (Mar 13, 2012)

This is gold.  Thank you!

Do you think there's any merit in inbreeding right away? Say, rex brother to sister? And selecting the does that don't develop the condition? She said it develops between 3-4 months. And again I have no qualms euthanizing sickly mice.

I only have the one line now, bred for type. I could keep it going but my mouse population would sky rocket. The only sister I kept has small eyes (and is PEW) so the only benefit to the litter would be having unrelated mice to the splashed line. I'm not sure it'd be worth it if the lines were never to be crossed as these pet store derived mice are years away from being a good standard.


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## PPVallhunds (Jul 26, 2010)

Yeah you can do that, I suggested the above as I wasn't sure how you felt about risking creating mice with the condition. If it was me I'd properly try to work out who was carrying it by inbreeding then if enough don't carry it cull the ones who do, if not enough I'd breed carriers to clears then test breed again to see if the amount of clears have gone up. The easiest way to test would be to keep a buck who has the problem and put him to the does if the does carries it you have a 50/50 chance of getting effected mice, so if none of the litter gets problem you can have a good guess the mother doesn't carry it (but you could just be unlucky and she does but none get her bad gene), you would also know any Baby from him not effected will be a carrier.

I'd also keep you type line even if you only breed it once in a while to keep it going as if disaster strikes and she does carry it and you are unlucky enough to later on end up with lots having the condition you could end up with with nothing.


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## Seafolly (Mar 13, 2012)

"I'd properly try to work out who was carrying it by inbreeding then if enough don't carry it cull the ones who do, if not enough I'd breed carriers to clears then test breed again to see if the amount of clears have gone up."

Sorry I'm slow! What do you mean by enough? Meaning if the majority of the litter doesn't carry it, cull the ones who exhibit, and breed one of the carriers to...wait how do I know if one's clear? x) Clear meaning a likely carrier but doesn't show it? I can buy a male and two females from the same litter, and see what happens there, though he hasn't shown the problem. Very interesting solution! I really need to look up CO2 tanks...I've been avoiding it but to properly continue my breeding I really need to be ready to remove unnecessary adults, particularly if ill.

Extremely good point about the safe line. It looks like I'll be breeding my satin PEW girl one more time (rather than her daughter with small eyes). : / Not exciting, but necessary.


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## PPVallhunds (Jul 26, 2010)

By clear I mean doesn't have the gene for the condition at all. I'd build up the numbers so you had a few adult does who ears didn't fall off, then test breed to try to work out who is carrying the gene and who most likely don't have it. If I had a good number of adult does who didn't have the gene I'd cull the adults who carry it, so I'd only have adults to breed who most likely didn't have the gene. If there wasn't many with out the gene or only a few I'd breed from does who carried it as well to get more adult does and test breed again later on in hopes of getting more does who most likely didn't have the gene.

To test for the gene, the most accurate way would be to inbreed and keep back a buck who has the ear falling off condition as you know he has 2 copies of the gene, breed him to the does and if they are carriers there's a 50/50 chance of producing babies with the condition. If they do you know that doe carries the gene. If none get the condition you have a good idea that doe doesn't carry it, however you could have just been unlucky and she did but none inherited it. So it's not fool proof but you get a good idea. You will also know that any babies from the test breeding who don't have the condition will be carriers so you can either keep or cull them depending on how any carry it and how many are clear.


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## PPVallhunds (Jul 26, 2010)

If you brought from her a brother and two sisters from the same litter and bred them tougher split up the does to birth so you know who had what babies as if any baby end up having the condition you will know both the male and the female who birthed that baby carry the gene. Then you can make a note that you know they are carriers. But it could be that none or just one of the 3 have a gene for it if your lucky. Or all if you unlucky, but if they all did you can still work to breed it out.
I'd also try to run on as many per litter as possible so you have a better idea what genes are there, as if say a doe had 9 and you kept back 3 pinkies, it could have been one of the 6 you culled may have had two copies of the gene and the 3 you kept either one copy or no copies. So you still wouldn't know if the doe was a carrier.

So breed them and keep back does who's ears didn't fall off, they will either be carriers or be clear (don't have a gene for it). Once you have a good amount of does test breed to see which carry it and which prob don't have it at all.


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## Seafolly (Mar 13, 2012)

Hmm, I'm going to have to think hard on it! Although I can see myself willing to cull any mice that develop it, I don't think I could breed one that for sure does (although I definitely see why that's a good idea). I'm leaning towards breeding the brother to the sisters and housing them separately for the reasons you mentioned, and hopefully breed it out that way. And yes, culling heavy here wouldn't be ideal I agree! It might be a slow process for me because I do cull bucks at Day 2 but I always keep does.

Thank you so much for your explanations!  I feel a little more clear on what I should do! When I get photos I'll post them up and see if the brother is worth bringing back.  I don't know of any breeders in the area, so whoever I adopt to wouldn't be spreading the gene (and I'd be sure to scare them with the knowledge of what they carry to be sure of it). Pet only homes for these guys once they pass the 3-4 month mark (when the condition shows up).


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