Your opinion on inbreeding

I've heard a variety of opinions regarding inbreeding corn snakes. I've heard some say that it's totally fine and won't result in any deformities whatsoever, while others say that you can only cross daughter to father & son to mother (not siblings). This topic has been bugging me for the past couple of days so I decided to ask about it here. What do you think?

Lisa

A lot of people inbreed. If you buy 1.1 of a morph chances are you are getting 2 siblings unless the pair is specifically labeled 'unrelated'. If you have a new snake morph pop up the usual way to prove if its genetic is to inbreed back to a parent. Or if you are working on a certain look, like I am with stripe and silver queen, you want to cross the siblings that have the look you want I am keeping a couple of pairs of siblings to experiment with this combination.
If there were no inbreeding we wouldn't have these terms like 'F2' . I think if you inbreed or line breed you do need to outcross every so often, by narrowing the pool you are also increasing the chances of recombining 'bad' genes. The inbreeding itself isn't what causes the deformities, I think its the fact the odds of the mutation showing up if its recessive increase. The mutation can be 'good' as in a new color or pattern. But it could be bad as well, so adding new bloodlines is a good way to help keep the strain robust. I don't know if this made sense or not but I hope that it helps.

My comments don't pertain to corn snakes specifically, but rather to inbreeding in general.

In the short term, inbreeding may very likely not produce any noticable problems. However, inbreeding increases homozygosity over time. This means the odds of creating offspring that are homozygous for deleterious alleles increases, because family members tend to carry the same alleles.

I don't really know what the basis is for saying it's okay to mate father->daughter or mother->son but not brother->sister as it relates to deformities. Parents are related to their offspring to the same degree that a full brother and sister are related to one another. In other words, parents share 1/2 their genes with their offspring, and full sibs (brother and sister) share 1/2 their genes. From that stand point, there is no difference in any of those crosses because they are all equally related.

A very good breeder friend of mine told me that she has inbred without seeing any ill-effects to the offspring (referring to breeding siblings to each other and father to daughter, mother to son etc)

But she did say that problems start cropping up with 4th generation inbreeding... (something like you can have kids with your cousins without ill effects but you run into problems when having kids with your parent's cousins/second cousins...?!?!?! Or something along those lines...

I am certainly not an expert by any stretch of the imagination so waiting to hear from those "in the know" as well!

The inbreeding itself isn't what causes the deformities, I think its the fact the odds of the mutation showing up if its recessive increase. The mutation can be 'good' as in a new color or pattern. But it could be bad as well, so adding new bloodlines is a good way to help keep the strain robust. I don't know if this made sense or not but I hope that it helps.

Mutations are very rare though - they happen so infrequently that it's not worth worrying about, what is worth worrying about are deleterious genes that your initial stock may carry already. By nature of the beast, genetic problems tend to be genetic (there are dominant genetic problems, but it is very easy to eliminate a dominant problem in one generation, and also animals displaying the type of genetic problems you would want to eliminate don't tend to be able to breed)

There are two main schools of thought - the first one is outcross, don't inbreed, to narrow the chances of recessive defects rearing their heads. The second way of doing things is to inbreed to make sure your animals don't carry any deleterious mutants - if they do, you can stop the line or fashion a test mating program to clear your lines of the "bad gene". The problem with just outcrossing is that in a finite world, outcrossing every generation forever is just not possible, and also, if you were breeding a line with a recessive defect in it, then by outcrossing you're producing loads of unidentified potential hets, which could end up being a problem way down the line.

Inbreeding doesn't cause genetic illness, and if you inbreed and get mutants and monsters then your original breeding stock had all those genes to cause the problems you're seeing now.

The only problem that is really caused by inbreeding is termed inbreeding depression. Once a population reaches a certain point of relatedness (I think it's due to the levels of homozygosity in the mating) then fertility decreases, clutch sizes will decrease, and the overall size of the animals can also decrease. It's impossible to say that X number of generations of inbreeding will cause inbreeding depression, and especially difficult when matings are not always brother x sister, but looser inbreedings such as aunt x nephew can skew the overall inbreeding percentage.

Unfortunately this is difficult to track in snakes as, over here at least, pedigree documents showing heritage seem to be non-existant. Just to show a comparison, in my rats I keep full family tree documents going back as many generations as possible (normally between 15-25 generations), and I have noticed that once you work out inbreeding calculations for a decent number of generations, a mating between brother and sister can actually be a lesser inbreed than a mating between two animals where there are no common names in the first three generations of the pedigree. So when you buy "unrelated pairs" of snakes - how unrelated are they really? You may find in some cases a brother-sister pair might be more genetically diverse :-)

I'd say in the wild that chances are snakes at least will have some inbreeding as their territories are not as huge as many mammals. Rattlesnakes for instance return to the same dens to give birth and hibernate. I'm certain related animals are at some point breeding. Snake breeders use inbreeding to establish colors and morphs too and I think if used moderately, it shouldn't be a problem.

I posted this response in the Reptilescanada forum when you asked there - but thought I would repeat myself here - even if it does repeat several points made above.

I think inbreeding is of great value in a breeding program when used to achieve a goal - especially with selectively bred traits - like candycane or reverse okeetee morphs - even more than with single gene recessives that are easy to select for.

In general, inbreeding will increase homozygosity in your stock - increase the percentage of genes (both desirable and undesirable genes) that are homozygous. Uncovering these undesirable genes allows you to identify and cull them from your line. The homozygosity also means that a highly inbred line will tend to produce offspring that are more uniform in appearance than an outcrossed line. This is a real advantage if you want to produce a particular 'look' to your snakes - so people can know by looking at the parents what the offspring will grow up to look like. Close inbreeding (between siblings) for many generations is used in livestock to result in very uniform lines of stock that give consistent growth rates, carcass composition and quality - they have culled out the weak genes from these lines and only produce highest quality at this point and they are extremely genetically consistent. This is also used in developing lines of laboratory animals.

Along with increased homozygosity comes the disadvantage of what is usually termed 'inbreeding depression' - the genetics associated with things that affect general viability - feeding response, general vigor, maternal functions - all tend to get worse when overall homozygosity is increased. This is in addition to uncovering undesirable genes. This 'inbreeding depression' effect is why intermittant outcrosses are desirable to maintain vigor in the population and why you need to monitor the vigor of your stock closely if you plan to inbreed.

In my opinion, the best circumstance is to begin a breeding program with genetically diverse stock - to breed your high value single recessive genes (male) into several genetically distinct line females (all of which have the vigor, growth and other general characteristics that you want)- and then combine those lines to recover your recessive gene morph animals. These morph animals can then be combined - either morph to morph or better yet by morph to het - to get morph animals that have a very wide scope of genetic material. This genetic diversity within a group of morphs gives you a great deal of foundation material to inbreed within. You can develop one or ideally a couple lines that can then be strictly culled to achieve the 'look' you are after and as you inbreed these you will achieve greater consistency and retain the ability to outcross between your lines, without having to bring in outside 'unselected' lines - and be able to counteract the decline in vigor that comes with inbreeding.

Check back with me in another 5 years or so and I will let you know how it is progressing!! Reality doesn't always align with theory.


mary v.

A couple of obvious points:

All modern animal husbandry is based on inbreeding. Basically all the food sources we have all heavily inbred. That's why we have turkeys so heavy they can't fly and cattle that are nearly twice the bulk of their ancestors. It's a good thing. But food animals are not bred for longevity. Hopefully pet animals are.

By definition developing new morphs requires inbreeding. What I haven't seen discussed here is "Hybrid Vigor" or the tendency that multi generation inbreeding results in smaller, weaker, less healthy specimens. I bred dogs, cats, birds, and fish before acquiring the snakes. All of those species showed the negative effects of inbreeding after five generations.

It's kinda three steps forward, two steps back thing. You inbreed to establish desired traits and then outcross to get rid of the bad stuff that shows up.

My family and I like it just fine thank you.

Originally Posted by jzal8

My family and I like it just fine thank you.

Originally Posted by bill38112

A couple of obvious points:

All modern animal husbandry is based on inbreeding. Basically all the food sources we have all heavily inbred. That's why we have turkeys so heavy they can't fly and cattle that are nearly twice the bulk of their ancestors.

There is a degree of accuracy here in that one could argue that animal husbandry (more specifically, animal domestication beginning thousands of years ago) is based on inbreeding to some degree. Additionally, many plant species are highly inbred.
However, turkeys so fat they can't fly aren't necessarily the result of inbreeding. It's important to make the distinction between artificial selection/selective breeding and inbreeding.

Originally Posted by bill38112

What I haven't seen discussed here is "Hybrid Vigor" or the tendency that multi generation inbreeding results in smaller, weaker, less healthy specimens. I bred dogs, cats, birds, and fish before acquiring the snakes. All of those species showed the negative effects of inbreeding after five generations.

This may be a valid observation and I'm not discounting that you observed it, but it does depend on at least a few factors. The species in question, individual's relatedness, and the initial frequency of homozygotes all can change how soon you will notice things. A group of animals that have high heterozygosity to begin with are going to take longer to show inbreeding depression. Some populations will take less time depending on their initial size.