Missing morphs 1: Enchi + any 8 ball gene, Albino Fire

http://ball-pythons.net/forums/showt...24-Albino-Fire

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Originally Posted by TessadasExotics

one locus can affect another locus or even attach to it.

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A locus cannot “attach” to another locus.

Quote:

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Originally Posted by Kurtilein

Yes, exactly! The distance between two genes on the chromosome determines the chance of them crossing over. Often chromosomes, during reproduction, break and get fixed which can exchange a part of the chromosome. When two genes are close together or at the same spot, and such a break/crossover/linkage occurs, chances are low that they are affected, the genes will only be affected by such an event if the breaking point is between their locations. (im really not good in the terminology....).

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Okay, we are on the right track here.

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Originally Posted by Kurtilein

My point is: EVEN IF two genes are on opposite ends of a chromosome, meaning they will be affected by every one of these chromosome-breaking event, its STILL rare, very rare, can only happen when regular cells split into sperm cells / egg cells, once per generation. ive heared numbers, varying, cannot remember them, but ill just limit it in one direction and say it happens in 1 of 1000 eggs at most, its probarbly more rare than that. ill also read up on this stuff, its been a while since i really studied it.

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But here is where you are starting to get a little off track but I can see where/how that happened so let us see if we can go about rectifying it. The biggest hiccup here is because of your odds, the ones you are operating on are way too low. The rate of homologous recombination during meiosis is not 1 cell in 1000. The rate of homologous recombination is between 1% and 10% per homologous region. The final part of that is important; the rate is relative to the number of regions of homology, not the number of gametes that are produced. Now, given the number of chromosomes in the organism (18 in this case) and the amount of homology between said chromosomes it is fair to say that pretty much every gamete produced during meiosis is going to have genomic material that has undergone homologous recombination.


But, even with high rates of homologous recombination you still have the distance matter to deal with. I was able to find my slide deck so let us jump to that. As a caveat here, I made these up a few years back during a similar discussion about the True Ghost (i.e., Axanthic Hypo) and I really did not feel like reworking them in their entirety so that it was specific to the BluEL and BlkEL example I gave above. This is a hypothetical example only. I am not saying that this is how Hypo or Axanthic actually behave. The concept is the message here and it is the same regardless of the specific genes involved.


We will start with a case where the genes are proximal to one another

First, we breed a Hypo to an Axanthic
http://i146.photobucket.com/albums/r...ps7e865b79.jpg

And we get an animal that is double het for Hypo and Axanthic (blue chromosome from father, red chromosome from mother)
http://i146.photobucket.com/albums/r...psc87319f3.jpg

During the first stages of meiosis the chromosomes adopt their X form
http://i146.photobucket.com/albums/r...ps061b0373.jpg

And when they pair off we have a crossover event
http://i146.photobucket.com/albums/r...ps26b8a298.jpg

The chromosomes are then segregated
http://i146.photobucket.com/albums/r...ps217cf0b6.jpg

And our individual gametes are formed
http://i146.photobucket.com/albums/r...ps7cebc310.jpg

Now we repeat the process in another animal
Crossover
http://i146.photobucket.com/albums/r...psdfed5cc6.jpg

Segregation
http://i146.photobucket.com/albums/r...psf0f72ac3.jpg

Gametes
http://i146.photobucket.com/albums/r...psd2e6b20a.jpg


And then when we try to breed a pair of double hets we see that none of the gametic pairs available allow for us to have generate the double visual animal
http://i146.photobucket.com/albums/r...ps6f838ed2.jpg

The important lesson here is that, if we are dealing with two genes that are very close to one another on the chromosome, the odds of having the specific crossover event required to generate a gamete that carries both the recessive Hypo allele and the recessive Axanthic allele are very low (this could very well be the 1:1000 odds range). We then need to account that to get the double visual would require that this rare crossover event occur in two separate animals and that those rare gametes then manage to pair off.



Now let us look at a case where the genes are distal to one another

Again, we start by breeding a Hypo to an Axanthic
http://i146.photobucket.com/albums/r...ps0c18a9cb.jpg

And we get an animal that is double het for Hypo and Axanthic (blue chromosome from father, red chromosome from mother)
http://i146.photobucket.com/albums/r...psa3e4af8e.jpg

X-form
http://i146.photobucket.com/albums/r...psbf598492.jpg

Crossover
http://i146.photobucket.com/albums/r...psff66e0a7.jpg

Segregate
http://i146.photobucket.com/albums/r...ps5476ac55.jpg

Gametes
http://i146.photobucket.com/albums/r...ps0cc1474d.jpg

And repeat again in another animal
Crossover
http://i146.photobucket.com/albums/r...ps5d100dfc.jpg

Segregate
http://i146.photobucket.com/albums/r...ps58420ffa.jpg

Gametes
http://i146.photobucket.com/albums/r...ps96939ff0.jpg


Here, when we finally breed our double hets together, we can easily end up with a gametic pair that allows for the double visual to be produced.
http://i146.photobucket.com/albums/r...psbdf00cb7.jpg


The important thing to take home here is that, because the two genes are at opposite ends of the chromosome, it is quite easy to generate gametes that carry both the recessive Hypo allele and the recessive Axanthic allele. In addition though, the odds of a crossover event occurring are high enough that they effectively destroy any ability to make a correlation as to whether these genes are on the same chromosome or different chromosomes.


Put all of this together and what you come up with is what I was saying before: It is entirely possible for any pair of morph genes to be on the same chromosome with you not being able to tell. The only way you could know is if you happen to be dealing with a pair of morph genes that are fairly proximal to one another.

I agree with what asplundii wrote.

It was written earlier in this thread that ball pythons have 18 pairs of chromosomes. If there are 19 independent loci, then at least two of those loci are in the same pair of chromosomes. The last time I did a count on WOBP, there were over 50 loci. So many of those loci share a chromosome pair. But most of those are so far apart that the probability of at least one crossover event between two loci is the same as the probability of reshuffling independent chromosomes.

By the way, there is a possible linkage between salmon (AKA hypo) and motley in boa constrictors and another possible linkage Kahl albino and type 2 anerythristic in boa constrictors. I've been told of a possible linkage in leopard geckos, but I can't remember the mutants. But nobody has reported numbers. And a few hundred babies from the right matings are needed.

What I was talking about was linkage. Should have taken the time to express myself better I guess.
Genetic linkage is a direct consequence of the physical linkage of two or more loci within the same pair of DNA molecules that define a particular set of chromosome homologs within the diploid genome.

Great thread.