Reptile & Amphibian Forums

This post will address a genetics "problem" as well as a naming "problem".

We all know that theorhetically, a corn crossed with a california kingsnake produces an F1 junglecorn that is essentially 50% corn and 50% king, and should be portrayed as such. The problem occurs when two F1's are crossed to produce F2's, which we falsely dub "50% corn, 50% king". I'm sure you've already figured out where I'm going with this, but I'll explain in more detail for those who may not have realized this yet.

When you first breed a corn to a king, during "crossing over", the genes are randomly divided into halves and only one half of the mothers genes and one half of the fathers genes make up the genetics of the initial offspring. Either way, half of a corn is still "corn genetics" and the same with the king.

However, when crossing over occurs in F1 hybrids, ANY half of the genes may be passed on. Technically, an offspring of two F1 junglecorns could very well be 100% corn or 100% king, or ANY ratio of the two. Only the AVERAGE of the F2 clutch would be "50% corn, 50% king".

Take this example:
corn = c , king = k
cccccc X kkkkkk = ccckkk
(half of cccccc is ccc, and half of kkkkkk is kkk, so 100% of the offspring must be ccckkk)

ccckkk X ccckkk= cccccc, ccccck, cccckk, ccckkk, cckkkk, ckkkkk, kkkkkk
(half of ccckkk can be ccc, cck, ckk, or kkk; thus, each F1 can donate any percentage of either parent species DNA to the resulting F2's)

Is it okay to call an F2 hybrid a 50/50 cross?

And likewise, an F1 junglecorn bred to a "pure" corn or king (backbreeding) can still produce 50/50 hybrids in the same manner if the F1 happens to pass on it's "king" half of its DNA, or produce 100% corns. Again, the average would be 75% corn, 25% king, but the likelihood of any given offspring actually being 75/25 is very small since there are millions of genes, not just six.

Will it even be possible to establish breeds? How long could it take for a hybrid cultivar to retain genetics from both species and breed true? Or does nature have a sort of "fail-safe" mechanism to eventually revert hybrids back to their original species?

I'd really like to hear everyones take on this situation as it has bothered me for quite some time.

Thanx for listening!

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~Venom~

Hybrid Breeders Association

Well, thats a lot to think about...I have several Hybrids that I was sold as being 25% Pueblan and 75% Honduran, and another thats 25% Sinaloan x 50% Ruthveni x 25% Striped Cal King. I guess I can see my 25%/75% snake as a 50-50 hybrid that was mated to a 100% Honduran, diminishing the Pueblan heredity to only 25%. And I can even see where a 50-50 hybrid SinaKing is mated to a Ruthveni to get the 25%-50%-25% mix.

But, as you say, the amount of genes in these mixes can be variable to a great degree, I would think! We may, as Hybrid Breeders, need to either list the entire genetic husbandry of each snake, OR list them and name them by their genetic makeup only such as: Pueblan x Honduran, and not worry about the exact number of each parent...or we may end up with 31% x 69% mixes (on paper anyway)

So therefore, I would call my other Hybrid a: Sinaloan x Ruthveni x Cal King, and not worry so much about the exact amounts via parentage.

I like the names I have seen around, Sinacal, Sinacorn, etc. Maybe we can come up with more, I already call my pair Puebdurans!!

Anyway, good post, and hopefully those out there breeding or thinking about breeding Hybrids will be diligent in their record keeping and honest when selling the ones that are "Normal" looking.

Firstly, gonna answer this question: "Is it okay to call an F2 hybrid a 50/50 cross?" In this scenario it depends on whether or not the term 50/50 is correct. If the animal is the result of a F1 X F1 breeding then yes, you could accurately represent the animal as an "F2 50/50 intergrade". You aren't necessarily in this example saying that the animal indeed contains exactly 50% from each parent species, but that roughly 50% of its' genetic material is derived from each parent species. As long as it the "F2" is thrown in there, that should clear up any mistakes about the true genetic makeup of the animal. Remember, during the F1 and resulting F2 crosses you cannot(theoretically) result in 100% genetic material from only one parent species, the intergrade will be limited to within the boundaries (AKA 1%-99%) for either parent species.

So I guess the real answer to your questions is this, it is only a useful tool calling any intergrade "50/50" or "75/25", or whatever else, it doesn't mean the animal is exactly that, it is just part of the labeling to understand what ancestry you are dealing with.

Another thing I'd like to point out real quick before my lunch break is done is that in an F1 cross, the true percentage for each parent species genetic material is never exactly 50/50, you have to take into account common genes/alleles between the two, be able to differentiate between what does not occur in one over the other to even be able to come close to defining that, and this is something that isn't even able to be realized nowadays, which is why we just define them as F1 50/50 intergrades, F2 75/25, or F2 50/50.

Hope this helps,
Dan

I agree, using the 50-50, or 25-75 and so on, is only useful in establishing Ancestry of what has gone into the Hybrid. Still, it may be the only way we have of identifying our new snakes.

I am not sure how much importance it would be to me, when buying a Hybrid from a breeder, to have more in depth info than: Parentage, Possible Hets, and Possible Aberrencies.

First of all, it would be intergeneric hybrid for this example, NOT an intergrade.

Secondly, mathematically speaking, each F1 gets EXACTLY 50% of each parents genetics, and passes on EXACTLY 50% of its genes when bred. Now it seems quite obvious to me that it would be possible, yet not probable, that two F1 siblings could very well contribute the same half of their DNA to produce a 100% pure corn or king. Even greater odds of an F1 bred to a pure corn or king. But like I said, it's not probable.

Another thing I'm sort of seeing with this theory I'm developing is that it seems pretty logical that if, for example, a Honduran Milk Snake escaped into southern California and crossed with a California King Snake (a large concern to many purists), within a few generations, it is possible that the Honduran genes would dissappear rather than polluting and ruining an entire species. I think nature has a way of fixing itself. I'm going to quit rambling now...
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~Venom~

Hybrid Breeders Association

I definitely agree about the Honduran escapee theory, the Honduran genes would soon be diluted without fresh Honduran genes in the pool.

I truthfully dont know enough to comment authoritively regarding the 50% genes coming from each F1, your theory sounds as plausible to me as the other one, where it is impossible to tell how much gene information would be attributed by each parent.

Neat stuff.

I guess in theory the escaped honduran might contribute something that might be beneficial, maybe the cross would provide better camouflage, hybrid vigor, a scent that might be attractive to more suitors, etc and the crossbreeds might flourish. There would be some increased chance that those might share a den sight, or suitable habitat and not have to spread out too far and some back-breeding or sibling breeding could occur, and the whole process of natural selection is carried on again. The favorable traits would survive or thrive and maybe eventually the California type might be locally displaced with the Honduran influence. I was wondering if there has ever been any indication of American Indians or Mayans or whoever of keeping kingsnakes around the teepee to help protect the kids from venomous snakes or rats? Maybe they would pack up a few to take with them to release around the new camp? I bet there were young boys way back just as interested in them as we were, maybe that contributed to some of these very closely related kings and milks.

To begin with, no snake has millions of genes. Nobody knows how many genes a snake has. That hasn't even been figured out for humans. The quess for humans is 30,000-50,000. That might be reasonable for snakes as well but it is not likely to be more than that. At any rate, we are not going to find out until the cost of vertebrate genome sequencing comes down to a few thousand dollars per animal. That looks to be 5-10 years in the future.

However many genes a snake has, most are pretty much irrelevant with regard to phenotype. These are genes that affect the visible pheotype of all snakes in essentially the same way. Genes that carry on essential cell functions, for instance, can vary slightly from species to species but it makes no difference in how the cell functions work. For the snake breeder, it is the genes that affect growth rate, color, pattern, shape, hardiness, behavior and fertility that are important (If I forgot an important component of the phenotype, feel free to add). This reduces the number of genes one has to consider to a still large but realistically manageable number. The problem comes in identifying them and determining how they interact. A number of genes are known, of course, at least for the cornsnake. What is needed is a website with a comprehensive list of properly identified and symbolized genes for the various species of snake and descriptions of how the various alleles of these genes interact, including how they interact in hybrids.

Bigfoot

""A number of genes are known, of course, at least for the cornsnake. What is needed is a website with a comprehensive list of properly identified and symbolized genes for the various species of snake and descriptions of how the various alleles of these genes interact, including how they interact in hybrids""

Aleady working in this direction if people submit their breeding data to HBA we might get there sometime soon.
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Adam
Hybrid Breeders Association

In response to this....

"For the snake breeder, it is the genes that affect growth rate, color, pattern, shape, hardiness, behavior and fertility that are important (If I forgot an important component of the phenotype, feel free to add)." - Bigfoot

Well, I would say that as a "working" definition, that works pretty well but is in general a bad genetic definition of what a phenotype is. Think about it this way, the genotype describes individual, or small groups of genetic traits, and the means of inheritance. Phenotype on the other hand, is a description of ALL the genotypes working together. The phenotype is in essence the end result, good example would be Graziani's het pieds(spider het. pied, pastel het. pied, link here: http://forums.kingsnake.com/view.php?id=1016293,1016293 ). Now normally only one copy of the pied gene will result in no phenotypic change, but paired with the pastel or spider it IS changing the phenotype, creating an intermediate between the two.

Hope this helps,
Dan

"Well, I would say that as a "working" definition, that works pretty well but is in general a bad genetic definition of what a phenotype is."

I wasn't trying to define the phenotype. One would hope anybody trying to breed plants or animals for specific traits would already know the rudiments of genetics.

I am rather concerned about what one finds on the internet with regard to snake genetics. I googled up a list of websites, the first page of which were atrocious. The top one was using B for black and b for white. To begin with, anybody who's bred snakes knows that black is NOT the genetic opposite for white. Secondly, at least in ratsnakes, Black is not dominant to nonblack. My guess is that it is polygenic but I won't find out until I get F2 progeny from my orange x black cross. Paul Hollander did have some cornsnake genetics on the web - with proper gene symbols and proper phenotype descriptions to go with them - but I can't seem to find it. Considering Paul's geneticist father was a stickler for proper terminology, we can be sure whatever Paul has done has been done right. If we can, we need to get it on the web and extend it other species and to hybrids.

Bigfoot

Here goes my attempt to answer this.... hope it helps.

First things first you need to adjust your focus to the chromosome level of genetics. One of the first things you’re going to need to understand is how chromosomes segregate during meiosis. I'm going to simplify this a lot because I don't really want to make the post super long but let me remind you this is not a simple case of inheritance that should be calculated out on a punnett square.

In the Elaphe decedents such as Cornsnakes and Kingsnakes they have a total chromosome count of 36. During the formation of the gamete cells these cells start to divide the chromosomes will separate into maternal and paternal chromosome sides 72 in all and recreate the missing maternal or paternal side of the pairs, then segregate into 2 parts mixing the information from the individual maternal and paternal chromosomes at random into 2 new cells each containing 36 pairs. The next step these 2 secondary cells divide again into 4 haploid gamete cells containing 18 chromosome halves which contain both chromosomes from the maternal and paternal sides. Again there is no real set order to which of the parental lineage’s chromosomes will end up in the final gamete cell. There is roughly a 50% chance on each individual chromosome half that it will make it into one of the 2 new cells this is then further reduced by a second 50% chance on the final split.

Secondly while this is happening there is also the chance for chromosomal crossover. When chromosomal crossover occurs a section of the two matching parental chromosomes break off and rejoin the opposite parents chromosome which creates two new chromosomes that further serves to intermix the genes of both parents. It is due to this chromosomal crossover that makes it impossible to say that you can breed back to 100% the odds just aren’t there. This is because each of the 36 chromosomes has the possibility of crossing over and can do so at any of the base pairs present in the chromosome. Generally, each chromosome will usually have at least one and no more than a few crossovers in each occurrence of meiosis. This exponentially increases the possible genotypes from a single pairing.

This will make a little more sense as I continue as I will show you the odds without the effects of chromosomal cross-over because I don’t know the number of base pairs in each chromosome. The number of possible combinations just out of meiosis is roughly N = number of chromosomes ((N/2)^(N/2)) which gives about 262,144 chromosome combinations for just one haploid gamete cell. If you take that calculation and then express it as ((N/2)^(N/2))^2 which you get the total number of possible combinations possible in the offspring of any two parents 68,719,476,736 if we are talking about hybrids out of that 68.7 mil 2 of the combinations would be pure. Which would give you roughly these odds, 1 in 34,359,738,368 in getting a pure animal back in a F1 x F1 breeding.

The information related to 50/50, 75/25 percent mixes is just a lineage based estimate which is not an accurate indicator of what the genetic mix really is. I would say that it would be better to say that a F2 hybrid is from a F1 50/50 x F1 50/50 cross then just saying it is a F2 50/50. Accurate information is important in any breeding program. The more information you give when selling an animal the better of the breeder receiving the animal will be.

Nature does not have a fail-safe to revert hybrids but it will use any additional genetic information and incorporate it the best it can into the populations genetic diversity.

When you are establishing breeds what you are basically doing is trying to fix certain genes in the population while removing others. If you want to know how long it will really take your going to need to do a lot of reading in population genetics. The process of getting a hybrid to breed true is basically in removing the excess variations out of the breeding program. What you essentially do is look for the dominant and hom recessive traits and by breeding those together repeatedly you artificially set up an isolationist breeding program to increase the frequency of those genes within the breeding population. As this happens, the phenotype of the hybrid genome will begin to breed true just like it would in an evolutionary occurrence which produces genera, species, and so on. Eventually the phenotype will become the hybrids genome and when this happens you will have a hybrid cultivar.
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Adam
Hybrid Breeders Association

Adam,

Luckily I do understand most of the genetic info in your post, and agree that there is a great deal more than identifying our Hybrids as 25%-75% of 2 purebred snakes.

However, aside from examining the exact DNA of each snake, it seems like we will need to come up with some sort of middle ground to identify our Hybrids, right?

It would be awkward at best to discuss our individual Hybrids on this board in specific genetic terms, especially if we have no way to determine which chromosomes have been passed on by which parent.

At this point I have only 5 Hybrids, but have over 80 eggs incubating from this springs breedings. Have you any ideas how best to describe my future Hybrids, other than 50-50 crosses of the parents?

Thanks, Scott
Origin Reptiles

Hi Scott,
I’m glad that you got the concept.

Hopefully within the next decade we will be able to get home DNA kits that can hook up to our computers so we can really see what goes on. However until then the only method I could say would work for us in identifying our hybrids is using a lineage based records and morphological examinations of the emerging phenotypes for common patterns in each new clutch. The way to do this is by keeping very good records backed up with photos of the parents and entire clutch. This is a huge part of what we’re trying to do on HBA by getting members to submit their breeding data. This way we have more eyes to look for the hard to spot traits that could lead us into a better understanding of what is going on genetically.

While it would be difficult to spot what exact chromosomes get past to the offspring we can look for individual traits. These traits are nothing more then one or more alleles that occupy a given locus on a chromosome. Then when the technology comes about we can use those traits as genetic markers to look further into the inner workings of the individual breedings.

The best way I could tell you to describe your future hybrids is to do this:
F1: (Sex) phenotype (50% species x 50% species) from 100% Male Phenotype (species info) X 100% Female Phenotype (species info)

For the phenotype info you need to include any morphological traits of interest such as: Color, color repetition, banded, blotched, or some other pattern, belly color, belly pattern if any, morphs, size, weight, eye color, plus any other unusual traits. This is a brief version of what could be included.

Don’t forget to add the sex of the parents. Some traits can be sex linked so it is important to be able to track these as well.

If you’re wondering about F2s and other mixes just adjust the fields to fit the need but the same type of information should be included all the way back to pure. It might seem like a bit much but if you are working towards stabilizing a hybrid to be a cultivar that breeds true all of that information will come in handy down the road.
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Adam
Hybrid Breeders Association