Breeding for breeding stock

I've been wondering generally how many inbred generations you can have with cornsnakes before one starts to notice problems. I mean, it's common practice to take 2 siblings het for a desired trait and breed them to get homozygous offspring... is it a problem then to take 2 snakes out of <i>that</i> pairing and breed them?

<table border=0><tr><td width="15">brother</td><td width="5">X</td><td width="15">sister</td></tr><tr><td width="15"></td><td width="5"><font color="red">|<br>V</font></td><td width="15"></td></tr><tr><td width="15"><font color="green">brother</font></td><td width="5">X</td><td width="15"><font color="green">sister</font></td></tr><tr><td width="15"></td><td width="5"><font color="red">|<br>V</font></td width="15"><td></td><tdwidth="15"></td></tr><tr><td width="15"></td><td width="5"><b>F2</b></td><td width="15"></td></tr></table>

Are genetic defects/weaknesses going to start showing up in the F2, or can it go more generations? Or, would be better (and more time consuming!) to breed the first set of offspring out to other animals (instead of breeding them together to get the F2) and get hets, breed those hets to siblings to get the trait in queston from two sets, and then breed those sets together as breeding pairs?

<table border=0><tr><td width="15"><font color="green">brother</font></td><td width="5">X</td><td width="15">new</td> <td width="15"></td><td width="15"><font color="green">sister</font></td><td width="5">X</td><td width="15">new</td></tr><tr><td width="15"></td><td width="5"><font color="red">|<br>V</font></td><td width="15"></td><td width="15"></td><td width="15"></td><td width="5"><font color="red">|<br>V</font></td></tr><tr><td width="15">brother</td><td width="5">X</td><td width="15">sister</td> <td width="15"></td><td width="15">sister</td><td width="5">X</td><td width="15">brother</td></tr><tr><td width="15"></td><td width="5"><font color="red">|<br>V</font></td><td width="15"></td><td width="15"></td><td width="15"></td><td width="5"><font color="red">|<br>V</font></td></tr><tr><td width="15"></td><td width="5">new</td><td width="15"></td> <td width="15">X</td><td width="15"></td><td width="5">new</td><td width="15"></td></tr><tr><td width="15"></td><td width="5"></td><td width="15"></td><td width="15"><font color="red"> |<br>V</font></td><td width="15"></td><td width="5"></td></tr><tr><td width="15"></td><td width="5"></td><td width="15"></td><td width="15"><b>kids</b></td><td width="15"></td><td width="5"></td></tr></table>

Or is there a better way to go when starting out with only 2 related foundation animals?

Dawn

I asked a similar question on here and to various collegues. I have been given mixed answers (NEVER breed siblings to its fine to do so). The way I see it it that its OK to breed siblings but not excessively down generations. Thats just theory...maybe someone here would be able to give you fact??
HTH anyway!

There IS no definite answer. It depends on the genes of the parents.
Lets say that a snake has, for instance, a wild, unpaired gene for a lack of eye formation.
If that gene is never paired with one to bring it to the phenotype, you'll never see it.
However, the gene for kinked-ness is more common(there are more carriers for this trait), therefore, some snakes are born with kinked backs. Also, how can you be sure that the first abnormality is not stress or husbandry related? it takes several breedings (years) to see if the "bad" gene does prove true.
Many times in the wild, a malformedsnake will die quickly, thus eliminating the phenotype from the population.
All this said, if you hit the right combo, deformities will spring up happily.
And, the more you inbreed, the better chance you have of seeing recessives.

Well, assuming the negative mutation is a recessive gene that only one parent carries, the earliest you'll get it showing up is in the F2's. The odds are the same as getting a lavender if you were to take a snake het for lavender, breed it to a normal, and then breed those hatchlings together.

If you breed an F1 back to the parent with the bad gene with one copy of a bad gene, then the offspring of that pairing are atleast 50% possible het for the bad mutation, and if the F1 you're using also carries the bad gene, then your odds increase of getting one copy, and you can even get both copies.

If we assume that any bad trait that shows up in offspring produced by a breeder is culled from the stock before any hatchlings are sold to the public (which isn't always true... but for the sake of this arguement we'll pretend all herpers are responsible), then we can assume that the only chance of a bad trait appearing is due to recessive genes. Ergo, a particular snake is at most het for the bad trait as an unhealthy snake would have been culled already. So... we buy a brother and sister of a clutch. For any particular bad trait, they're at most het. If both of their parents were het for that bad trait (worst possible case as homozygous ones are culled), then they've each a 66% chance of being het for that bad trait. If only one parent was het, then they've each a 50% chance of being het for that bad trait. Obviously if neither parent was het for that trait, they both lack it as well. Someone might want to check my math, but if the odds of the four combinations of parents (het/nothet, nothet/het, het/het, nothet/nothet) are equal, then there's roughly a 41% chance of any particular snake having that bad gene in the F1's. I sincerely doubt the odds are equal though... Depending on where you're looking, certain populations may have a greater chance of having the gene than others.

It's anyone's guess, really.
-Kat

These really disabling mutations that we're talking about don't seem to be simple recessives, since often only an inordinately small percentage of a clutch seem to be affected. Its like a rider gene that only occers if a combined # of other alleles fall a certain way.
Still difficult to project.

Thanks... I understand the theory behind the accumulation of genetic anomolies that can come from inbreeding... (Shaky, likely that is what it is.... a number of genes all have to be homozygous recessive before those major effects are evident) I guess what I'm really wondering is what the average # of generations is that cornsnakes can go without detrimental effects.... it does seem that some animals are more likely to have difficulties sooner with inbreeeding/line breeing than others, generally having to do with the sheer #s of genes and therefor the number of hidden recessives that could be present.

And, to boil it all down..... what's the most effective strategy for developing a wider breeding stock out of only two individuals who are het for a trait? Or out of only two individuals who are displaying a desired recessive trait (eg, if you only have 2 amels)?

If the lineage of a snake is unknown is there anyway to figure out if it is het for anything besides breeding?

"If the lineage of a snake is unknown is there anyway to figure out if it is het for anything besides breeding?"


No, not for certain.

However, many bloodred outcrosses are very red in their coloration and have distinctive ventral checkering patterns. Of course that brings up the old "Can a snake be het for bloodred" argument. I have also had some say that animals het for some strains of motley tend to have an effect on the F1 appearances, but I can't clearly recall who said they had noticed such.

Clint B., perhaps?

Hi Dawn,
You pose some interesting questions and I can't respond from knowledge of cornsnakes, but do have a couple ideas to share.

Besides uncovering hidden detrimental recessive genes with inbreeding, it is worth considering the depression of vigor that is associated with inbreeding and in mammals at least, seems to have most impact on the ongoing reproductive performance in females as the degree if inbreeding increases over several generations.

To perpetuate a recessive trait if you have only two siblings that show it, you might want to consider using the male to greater advantage by breeding him to several females, including the related one. All offspring from the breeding of siblings would produce snakes that show the trait, but were inbred. This clutch could be the source of a couple males for the next generation.

The outcrosses to normal females (unrelated to him and each other), will produce 100% hets which will have the advantage of hybrid vigor, and that has most impact on maternal characteristics, such as fertility. Keeping females from these outcrosses (het for your desired trait), and breeding them to the inbred males will give you quite a bit of genetic diversity in your next generation, along with 50% of the animals showing the desired trait. The offspring from the third generation can then be bred back to a brother that was not their sire (their uncle, or their grandfather) and you could be producing a very high percentage of the desired trait, while still maintaining a relatively low level of inbeeding because of using multiple females in the first generation. Continuing this process, using your second generation males on other normal females, and then rotating your crosses, will let you keep inbreeding down - the only real risk is if the original male carries some very bad genes that will be concentrated over time with this approach and come back to haunt you in the future generations.

I would also be very interested to know if breeders have had success with more than 2-3 generations of sibling breedings. Know it works fine in poultry and mice, but haven't read much about it in corns.


Just some thoughts,

Mary v.

For answer to if breeding brother to sister has been sucsessful just look at any cornsnake other than normal!

Most all morphs had to be inbreed originally to achieve the look they have today.


bmm