Reptile & Amphibian Forums

Brian,
Hope you don't mind but I have a question for you.

I think it was you that once mentioned that if you breed back a hybrid (or a cross)to one of the original parents enough times its DNA will be indistinguishable from a pure specimen.

How many times must one breed back to make the other species or sub-species undetectable?

Rainer

I did mention something to that effect, but I don't think my original point was ever understood. What I intended to express was that the level of testing that was available two years ago, and three years before that time when I was looking at haplotypes in Gallus domestics, could not have revealed more subtle differences. There may in time be techniques that could really reveal on a molecular level, a hybrid event, for many many generations to come. At this time, we are nowhere near that. Thus, "masking" genetic differences can be accomplished through "backbreeding", which is taking the hybrid f1 back to one of the parent forms and then going in that direction for generations. In some of our very simple tests, for instance MtDNA, this factor can be manipulated in this manner. For instance, if you take your male f1 hybrid and breed it back to the female of the species whose MtDNA you want represented, you will then pick up that MtDNA and all that generation will show the MtDNA of the special form in question. This does not mean that this animal is then "pure", but that on the MtDNA level, it would be indistinguishable from "pure" forms of the MtDNA line. For instance, in laymans terms, if I choose to make a jungle corn and I breed a male cal to a female corn, I get f1 hybrid, junglecorn which has MtDNA of corn, but is 50% genetic material from each parent. If I want my MtDNA to say "cal", then you take the f1 jungle (corn MtDNA) back to a female cal and all those offspring show "cal MtDNA". This always works this way and shows the limits of MtDNA as a major marker factor in genetic work. It is in the nuclear DNA that the real story is happening. Except for the sex-linked genes at the X and Y chromosomes, all these genes are based on the many, many alleles on the chromosomes. You get one half of your total package from each parent, so the first thing to consider is that closely related lifeforms (and these snakes which can produce fertile offspring definately are closely related) may share almost all of their genetic material in common. We share 98% with chimpanzees, so imagine how much closer it is in say ratsnakes and cornsnakes or the various forms of getula. Thus you really dont have that many variable alleles. The variations at thsoe alleles may be great, especially depending upon the distance in time from species split behind the two forms, but those which can produce complete fertility in their f1 offspring are not very differentiated , thus probably not very far apart in time, as their seperate evolution goes. Thus you would require a complete gene map of each parent species (as has just recently been finished in humans and poultry, at considerable expenses)to look for any variations in the genome. This would then be your markers. It is by looking for markers that genetic difference is notated. Back breeding and selection can allow you to go back to complete genetic "purity" (i.e., a complete match to the original genome of either parent form) by using molecular markers in each generation to narrow and weed out the genes remaining from the alternate parent forms. However, this would require access to a full mapping of both original species and the ability to map the offspring for comparisonin each generation. At our current level of knowledge we could accomplish this. However, applying it to our hobby animals is unlikely, as this is an very costly process.
Using the simple markers that are generally used at this time in all animal registries and "DNA fingerprinting", outcrosses can vanish from the record, even on a molecular level relatively quickly, as per the testimony of those given tests. If selection toward the visual phenotype of the desired type is made, you will end up with an animal which is visually indistinguishable from the pure species, and it is even possible to mask the hybrid origin on gene tests as well, if you know how to get around a certain test, such as the MtDNA test, and you are dealing witht he simple tests which are more available at this time.
Finally, I think this information is actually counter-intuitive to what I wish to see happen. I think conservation of pure forms is fantastic. I just personally have no interest in it what so ever. What I think the hybrid community needs to be focusing on is moving forward with true domestic strains, that have nothing to do with "wild types" (which should be part of conservation). The hybrid strains, which in time will be simply "domestic colubrids" or something such, can compliment the moprph forms of pures in the hobby and pet trade, and can allow the complete closing down of wild catching, which it is simply beyond belief that this is allowed to continue, when so many wonderful things are happening with captive breeding, both through morphs on "pures" and with hybrid strain development. One thing my research has shown me is that all the best stories and all the best data can never confirm beyond a shadow of a doubt that something is "totally pure", but I think it gives one pause to consider the rapid emergence of so many morphs so suddenly in captive breeding.
I hope this answers your questions Rainer. Thanks.
BR
Feathered Serpent Productions

I appreciate you taking the time to answer my question!

Now I realize that my next question is highly debatable and I am not trying to stir the pot here but get an idea with curent testing in place, if you knew how many times backbreeding needs to be done before an animal goes back to its parent form? I know there will always be a percentage but I am talking about the current testing we have avaliable.

I remember something about livestock and breeding back to what is accepted as a pure form (maybe cows or chickens?)not sure if I remember correctly but I am hoping to get a number of times (2X?,3X?,4X?) considered by farming standards to make a possible comparison?

Good stuff. Much appreciated Brian!

After reading your post over I relize there can be no hard and fast rule to the number of times backbreeding is done. Sorry about the stupid question. You more than answered it.

I guess simple minds always look for the simple answer.

No problem. Your welcome.
BR