Rexed Fur Probability?

[jaxmarblebuns]

I have been trying to figure out how exactly the Rexed fur genetics work, and I’ve found some information but nothing definitive enough for me to be satisfied.

So, what percentage of Rex do you need for the off spring to start having Rexed fur?

For example, I know that a 50/50 cross (Rexed/Normal) will only have normal fur.
So, if I take that 50/50 and breed it to a pure Rex will those off spring then have Rexed fur? Or will there at very least be a chance for it? Or are they still all going to have normal fur?

If it’s possible to lay it out in a chart like this

50/50 0% chance
75/25 12% chance
80/20 40% chance
Etc.

That would be most beneficial. Thank you to anyone that can help.

 

[Cosima]

I’ve been wondering the same thing.

 

[judymac]

Okay, for each gene, the rabbit has two alleles. 'Allele' is just a fancy word for a possible choice on a given gene, in this case the choices are two: the normal and dominant not-Rex fur, with guard hairs extending beyond the medium-length fur, coded with a capital R because it is the dominant choice; and the recessive short, plush rex option, which is coded with a lower-case letter because it is recessive. Each parent donates one allele of the gene to their offspring, so each kit has two copies, it's pure chance which one each parent donates.

Only one dominant allele is enough for that trait to be expressed, so either a pure non-rex RR or a non-rex with a rex recessive Rr will look the same, they've both got normal fur. Rex is a recessive trait, that means you need two copies of the rex recessive allele for the wonderful dense, short, plush fur that keeps the guard hairs from extending beyond the down fibers, to show up.

So, let's see what happens when you cross a normal non-rex with a rex, illustrated in a Punnett square. You put the alleles of one parent across the top (in the yellow boxes in this case, and the other parent on the side (blue boxes here). It doesn't matter which is the buck or doe, it comes out the same. Where the rows and columns meet, you put in the results, for example, you carry down the top parent's 'R', and carry across the left parent's 'r' where the two cross. . .where they meet will be the genotype (what genes they carry) of that kit. In this case, it is Rr, which means the kit is dominant non-rex but carries the rex recessive.

This chart is presenting odds. Each of the four boxes is a 1 in four chance, 25%. Here, the results are the same in all four boxes, so there's a four out of four, or 4 x 25%, or a 100% chance of non-rex kits that are rex carriers.


Remember, this is pure statistics. Don't take Lady Luck out of the picture. As any gambler knows, things often run in streaks. (Even though the odds of male to female are roughly 50/50, I had one litter of all bucks, and another of all does this year. Lady Luck at work). So, your half-rex mated rex offspring have a 2 out of 4, or 50%, chance of being normal-furred but carrying the rex recessive, and a 50% chance of being rex. Woo hoo!

You can use this same technique with other traits, such as dominant black 'B' vs. recessive chocolate 'b'; dominant agouti 'A' vs recessive solid self colors 'a'; dominant spotting 'En' vs not spotted recessive 'en'.

 

[user 8761]

To back up judymac’s answer, I recently bred a Rex/NZ to a Rex and the litter of 7 kits has 3 Rex furred, 4 regular furred kits.

 

[judymac]

So, the answer to your chart request, is that in the first generation, you have:
50/50 0% rex, 100% normal fur but carrying rex recessive, 0% pure normal fur

Every generation thereafter will be the same odds, as you will always be mating a rex with a normal non-rex that is carrying the rex recessive:
50% rex, 50% normal fur but carrying rex recessive, 0% pure normal fur.

So, theoretically, even though pedigrees are set up so that after three generations of breeding back 'pure' you technically have a purebred, this could happen:

1. Pure rex x non-rex first generation kits will all be non-rex carrying rex recessive.
2. Mating a kit from gen 1 to a pure rex gives a 50/50 chance of rex, the rest will be non-rex but carrying the rex recessive. If you choose a rex kit, and mate it rex, you will have a 100% chance of rex offspring, and your search for a 'purebred' pedigree is on its way. BUT, if you choose one of the second generation non-rex kits as the parent of the next generation. . .
3. Mating the non-rex kit from gen 2 again gives you the exact same odds, Rr x rr, and again you have a 50/50 chance of rex. Again, if you choose a rex kit, you'll be on your way to 100% rex offspring. BUT, if you choose a non-rex kit as the parent of the next generation. . .You could breed hundreds of generations this way, and still not have a guaranteed rex. So, while the percentage of purebred rex on the pedigree would go from 0% for the non-rex parent, to 50% in the first generation (you add half the difference between the two each time you breed to a purebred parent, so the difference between 0 and 100% is 100 divided by 2, or 50%, I'm rounding in the rest of the calculations). 75% in the second generation 87% in the third generation, 93% in the fourth generation, 96% in the fifth generation, 98% in the sixth generation, 99% in the seventh. . .

So, pedigree 'purebred' and actual genetic purebred are two very different things. You could have a hundred generations bred to pure rex, and still only have a 50/50 chance of rex offspring should you keep choosing a non-rex but rex carrier kit as the next generation's parent. Or, you could breed non-rex but rex carrier 1st gen hybrid to a rex, get a rex offspring, and then breed to pure rex and have all rex from then on.

No matter how many generations bred back to purebred you have, each time you breed a non-rex but rex recessive carrier Rr to a pure rex rr, your odds are always the same: 50% rex, 50% normal furred non-rex but carrying rex recessive.

This is why the Vienna blue-eyed white genetics can be so difficult, often causing the white mismarks that disqualify for showing and registration when hybrid (Vv). In the first year's cross of Vienna BEW 'v' x non-Vienna 'V', you end up with 0% BEW, 100% non-Vienna but Vienna carriers, and 0% normal 'VV' offspring. That means every single bunny is a carrier. When you mate back to non-Vienna dominant (different than your example of breeding to a recessive rex), you get no BEW babies, but half of the offspring still carry the Vienna recessive allele, even if they are not mismarked. EVERY generation of those Vv kits bred back to normal non-Vienna rabbits still has a 50/50 chance of throwing more Vv carrier kits. So, you could breed the BEW right off the pedigree, and still have mismarked kits with white toenails or white marks on the face show up.

 

[Keag]

Just to throw a wrench in genetics I got a Rex coat out of 2 "normal" parents. Out of 2 litters, 10 kits, 1 Rex. This was a total surprise and I believe this was a brother x sister breeding, ( I received rabbits 2nd hand & were told all female). I absolutely love this little plush kit.

 

[kusanar314]

Just to throw a wrench in genetics I got a Rex coat out of 2 "normal" parents. Out of 2 litters, 10 kits, 1 Rex. This was a total surprise and I believe this was a brother x sister breeding, ( I received rabbits 2nd hand & were told all female). I absolutely love this little plush kit.

Not very surprising honestly.

Recessives can be sneaky and hide for several generations.

 

[judymac]

Yes, this sure can happen with recessives. Since they had a recessive rex kit, we know both parents are rex carriers. Since neither look rex, we know they also have dominant normal fur, so each must be Rr, normal fur with rex recessive. When they are mated, these are the possibilities:

 

[Keag]

Just a pleasant surprise.

 

[Rosey1]

Just to throw a wrench in genetics I got a Rex coat out of 2 "normal" parents. Out of 2 litters, 10 kits, 1 Rex. This was a total surprise and I believe this was a brother x sister breeding, ( I received rabbits 2nd hand & were told all female). I absolutely love this little plush kit.

Yeah I was gonna say I bred 2 New Zealand’s and got curly New Zealand’s which have the soft Rex feel. Then I have a boy who is half Rex, half lop and I bred him (or should I say he escaped and bred himself to my Flemish chin girl and their babies (9) majority had this very soft Rex fur. Not as plush as a full Rex, but as they are getting older it’s definitely thickening up and they look just like my other Rex rabbits. They are only 1/4 Rex. She only had maybe 4 of 9 with regular fur in her litter.
when I breed my curly girl to my boy with the recessive curly gene I get almost complete curly kits. She has 1 or 2 normal furred kits. When I breed my recessive curly mom to my recessive curly dad I get about half and half.

 

[judymac]

The curlies sound wonderful!

 

[Rosey1]

The curlies sound wonderful!

They are. They are so cute. When they are little they look like little sheep. As mine get older they lose some of the curl, but then as they hit adulthood they get it back and their head is the curliest.

 

[Cosima]

That’s not Rex fur that astrex fur.

 

[judymac]

True, the curlies are the recessive Wavy gene found in the Astrex breed, but it works the same way as the recessive rex gene as far as the probabilities go.

 

[Rosey1]

That’s not Rex fur that astrex fur.

I know it’s astrex fur, but I included it with the Rex fur gene as it works the same way. They came from 2 regular furred New Zealand parents I have Initially.