Breeding siblings together?

I thought sibling to sibling pairings were usually not recommended. I always hear it increases the chance for issues to pop up. Some of the babies will only have a 50% chance at being het for pied as well. And with that combo wouldn’t the result basically just be a white snake? Kinda a white wedding type of thing were genes are near impossible to identify.


Yea definitely aware of the 50% but not worried about it and I’ve never heard of those sibling issues unless its certain morphs or mammals


Snakes being non-migratory, inbreed frequently in wild populations.


It depends on the size of the population. They follow food, and don’t just stay in one place their whole lives. There is also a chance that the relatives of one snake will all die. If it is a large open population, inbreeding is not overly common. If it is a small closed population, they have a higher chance to. Trust me, I know a lot about that stuff. Inbreeding too much in populations leads to weaker animals. The closer they are related, the higher the chance of problems. That is why I always hear that siblings are best not to be bred together.


I have never had nor heard of any issues from breeding siblings. @jones810975 congrats on your new snake!! Very nice!


I’ll have to respectfully disagree.
On the small islands that locality Retics live on there is constant inbreeding. Retics dwell in caves on these islands and seldom go very far from their food source which is primarily bats in these caves.
Over the generations this inbreeding has made some theory’s that it’s actually made these snakes stronger genetically, not weaker.
I myself have heard no issues with inbreeding in ball pythons too, of course you start to inbreed into 3-5 generations I’m sure you can expect some problems. But the chances on a sibling to sibling pairing for defects or other issues is very low.


I suppose I could call in our geneticist friends to answer this, though I am sure the answer would vary depending on the situation. Does inbreeding lead to genetically weaker animals over time?

@chesterhf @t_h_wyman

(Feel free to move this into a relevant topic if needed).

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I would think that it could go either way — simply put, survival of the fittest, regardless of lineage.

Inbreeding produced stronger offspring? Great, they’ll do better in the wild and be more likely to survive into adulthood, and also pass on their genes. Weaker offspring simply would be less likely to survive.

My thoughts are that as long as the parents aren’t severely inbred, I don’t think there would be an issue pairing sibling x sibling.


Actually they do remain in the same area or at least very close proximity. Having spent many years doing my own field study, I’ve caught several snakes multiple years in a row within a 50’ radius, also while being in a very reptile populated location. If you knew how much of the entire reptile hobby was established by sib x sib and such, you would quickly see it hasn’t made a drop difference. There are decades of inbred lines in many collections and I’ve not seen any factual supporting evidence that points to negative effects. It mostly comes from the inbreeding of mammals in my experience. Inbreeding is what has established recessive genes in our hobby.

When it comes to lab rat/mouse strains, they recommend not outbreeding as it dilutes certain traits a particular strain is developed for. A friend of mine who has been breeding rodents for over 40 years just told me over the weekend he’s going on 13 years without adding a single outside mouse to his colony(1000sq ft). Same for his rats. He did spend $12.50 per mouse from Lily labs so he knew he was getting the most productive strain he could find. He did all of this with 5.20 adult mice and he produces around 20-30k mice per month.

Migratory animals are another thing. They come together from many different locations so new genes are introduced frequently. The mixing of lineage is frequent in migration.


It can also lead to genetically stronger animals in some cases.


I agree with this :100: as long as your culling the animals that turn out genetically weaker. You are in reality strengthing the colony. People need to realize snake and rats are not humans.


Line breeding to establish a trait for a few generations is pretty different than systematically line breeding an entire species. Genetic diversity is constantly being brought into the hobby through imports and crossing new morphs into older existing morph lines. If the person who originally started breeding albinos only bred those albinos back to each other for 20-50 generations without crossing out we would surely start to see issues caused by consanguinity. At that point the genome would pretty much be homozygous at every locus, which is not a good thing and does not strengthen the line. Look at purebred dogs, many breeds have incredibly high rates of cancer and other inheritable diseases. Inbreeding back for a generation or two is not a big deal, doing it continually is. A perpetually inbred animal is going to be genetically weaker than it’s outbred counterparts

Yes, my lab mice are incredibly inbred because they need to be genetically homogeneous to try and eliminate variability in experiments. They also have reduced lifespan, smaller litter size, prone to age related hearing loss and are susceptible to diet-induced obesity, type 2 diabetes, and atherosclerosis. I would never recommend inbreeding for a feeder colony as it reduces overall fitness of the colony and there is no benefit (other than maybe not having to go to the effort of bringing in new mice?)


So you don’t consider genes for litter size and adult size a benefit? What would the average lifespan be for an average mouse or rat?

With dogs, were again talking about mammals that travel long distances and roam. In my personal field experience with snakes, they USUALLY stay put.


It is a common trope in the hobby to see people claim that snakes are sedentary in the wild and, thus, inbreeding is not an issue. This is more a justification for inbreeding that it is based on fact. The huge range distributions of the species we are dealing with proves that they are actually pretty good at traveling around. When you further account for spacial, temporal and sexual distancing and how they relate to population dynamics then you come to recognize that inbreeding is not that common in nature.

There are exceptions - insular species/populations and the like - but they are exactly that, exceptions and not the rule

Lab mice/rats are the result if highly intentional artificial selection. They also tend to have shorter lifespans, reduced long-term fecundity, and develop cancers at an ungodly high rate because of a lack of heterogeneity brought about by systemic inbreeding. None of which tend to be observed by feeder breeders because of the turnover rate of the colonies.


I’ve seen a couple of breeders continually inbreed albino corns with zero issues for 30 years. Never a new animal from outside added. I didn’t say animals were sedentary in the wild, but they do den in the exact same locations every year in my experience. I get there are large range distributions but wouldnt those outlying population just keep spreading over time with increased population numbers? How about the Manitoba garter snake breeding. That area of the garter snake mass breeding isn’t very large at all and there are thousands of snakes mating together in a giant mass. Doesn’t seem like too much outside interference from new blood.

Just from my personal field experience, snakes don’t travel far at all in most cases. Just ask any legitimate graybanded king keeper about localities. The serious guys won’t breed animals that weren’t found on the same rock cutting.

Doesn’t that depend on the strain of mouse. I’m not sure how many there are but I know it’s quite a lot. My buddy that has done rodents for so long also worked in a research lab for 20 years, where his wife still works. He was told by Lily not to outcross because his strain was developed for high yield production and having adult mice at 60+g.


In my personal experience with snakes, they don’t stay put, as there is never consistently food in one spot year after year. Let’s say you have a severely inbred population, and you accidentally bring in a bacteria, virus, or something similar. If one dies, chances are others will as well as they don’t have enough diversity to have a shot at overcoming it. That is my understanding of how biodiversity effects the overall health of a population. Then again, I did learn my understanding through a video game called Niche that is based on real genetics, so maybe I am wrong. I just remember very clearly in the game, if you inbred your creatures and illness broke out, it was game over if you didn’t find new genetic materials to work with. I lost the game because it a few times.

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I was told that you could breed siblings together, or son/daughter back to the parents. However after you breed two siblings together you need to introduce new blood, or there could be issues.


You can can absolutely breed for traits like litter size and adult size without completely homogenizing your mouse colony through inbreeding. Pretty much anyone who breeds feeders is probably doing that by default and getting rid of poor breeders, slow growers, etc and not keeping them as part of their breeding program. You can apply selective pressure to a species without making them fully inbred. I was looking up mouse lifespans and it seems like in the wild they can live up to five years, although it’s usually less due to predation, and ~2-3 years as pets. Meanwhile I can assure you there are no mice in my (laboratory) colonies that are making it to 2 years. I usually euthanize at the 9months-1yr mark for my breeders because they get old, and frail and sad

Anyone who has ever lost a ball python in their house can easily attest that these guys can really go the distance if they want to. While I have no doubt that there is inbreeding occurring in the wild, there is plenty of opportunity for genetic diversity. Breeding back to a sibling/parent here and there is very different than perpetually linebreeding to a high degree of consanguinity. Biologically, genetic diversity is in a species best interest.


Taking that into consideration I don’t think 95% of hobbyists have to worry about outcrossing.


I was using that as kind of an extreme example, because it takes 20 generations of brother/sister matings to create a fully inbred mouse model, but even a few generations of inbreeding will create a pretty high coefficient of inbreeding.


There’s equations to calculate heterozygosity/homozygosity based on inbreeding coefficients so you could sit down and calculate after how many generations what % of the genome is likely to be homozygous (this is generally a bad thing), I just don’t have it in me to do it right now. Population genetics is not my favorite :joy: