Orange Ghosts: better in person?

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Originally Posted by RandyRemington

I wonder if some of the axanthic mutations are on the same chromosome as hypo making the combo even harder than the already hard 1 in 16. Maybe if not all the axanthic strains have been tried yet it would be worth trying a 2nd choice axanthic line.

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If axanthic and hypo were on the same chromosome (linked), then you would expect a better than 1/16 chance of producing the double recessive in a cross of two double hets (AaHh). Theoritically speaking, the chance could be as high as 1/4.

See

http://www.ball-pythons.net/forums/s...1&postcount=21

http://www.ball-pythons.net/forums/s...9&postcount=23

http://www.biology.arizona.edu/mende...cross/10t.html

I'll have to come back and do the tutorial link later as I don't have time tonight. I could see how after the crossover occurs to get both mutations on the same copy of a chromosome occurs you could get the 1:4. However, my thinking was that it would be hard to get that initial crossover.

If say VPI axanthic and ghost turn out to be on the same chromosome, when you create the double hets they would have one copy of the common chromosome with ghost and the other with axanthic, right?

Now depending on how close together the two locus are wouldn't the big problem be getting one, much less both, of the double hets to have an odd number of crossovers between the two locations to be able to give mutant versions of both genes to the same offspring? But by the same token if you ever did make a copy of that chromosome with both mutations they might stay together for a long generations and inherit like a single mutation.

Maybe I see the confusion. Does the term “linked” only apply once the crossover occurs to get both mutations on a single copy of the common chromosome and not to the general case of two mutations that exist in genes that are located on the same chromosome number but not yet combined in an actual copy of that chromosome?

Your original assessment was right. I thought I was off and I should have asked you for clarification and thought about it a little more..sorry about that.

However, it's good to mistakes--it often allows for a deeper understanding of the material and it allowed me to recall the difference between cis and trans linkage.

Linkage simply means the loci for the genes are on the same chromosome. So Linked genes are on the same chromosome. Pretty simple, right?.....Kinda but confusion like the one I had with Randy can be avoid by introducing a little bit more necessary terminology

The fact is there are two different "flavors" of F1 double hets for linked genes. You see there are two possible configurations, the cis and the trans configuration for linked genes.

cis and trans are used a lot in many fields of science. But "cis" means the "on the same side of" while "trans" means "opposite or not on the same piece/side".

The problem was I was I was thinking of a situation in which you crossed two "true breeding" or double homozygotes to get the F1 double hets. So in that case we would be crossing a Normal BP that was not het for either trait (AA HH) to a double recessive (aahh). This situation, analogous to the pea example described in the tutorial, would give you a theoretical rate of ~25%.

However, no double recessive or hypoaxathanic (aahh) has been produced to our knowledge. So that why my assessment was wrong and Randy's was right!

In a situation like this where no double recessive exists, the double recessive would be hard to initially produce if the gene loci were linked. But once it was produced, interestingly, it would be easy to reproduce because as Randy hinted the two loci would be inherited almost as if they were the same gene.


If you don't have a double recessive you have to try and make it, you'd do this just like you would for an unlinked gene. By breeding to make a double het....but the initial double het for linked genes would not be as useful as a double het for unlinked genes because (1) you cant rely on the independent of separate chromosome to produce recombinant or non-parental types and (2) it would be in the trans configuration.

In trans, the mutations would be on different homologous chromosomes. And as the Punnet square below shows mating two F1 trans double hets will never give you a double recessive unless you have crossing over event. Linked genes use slightly different genetic convention systems than unlinked genes. Geneticists often put a line above the two separate genes to represent a chromosome. Hopefully it's clear from below, that in contrast to unlinked genes, in linked genetics, you match up the non-homologous genes (non-matching letters) because they really do act somewhat like one large gene cause they tend to be inherited together.

https://ball-pythons.net/gallery/fil...nts_563135.jpg




Again, the double recessive would be hard to initially produce because you would be relying on cross-over between homologous chromosomes during meiosis I to get the axanthic and hypo mutations on the same chromosome in the gametes. The more closely linked-i.e the closer the the axanthic and hypo genes are on the chromosome, the smaller the chance of getting a cross-over that would produce the cis configuration. And it might be much less than 1 in 16 if the genes were very close on the same chromosome.


I hope this make sense at least for you Randy. Once you get the two mutations coupled (i.e. in cis), then what I said earlier and what is shown in the original Arizona tutorial on pea plants will ring true.

For a more historical introduction to this, see http://www.ndsu.edu/instruct/mcclean...e/linkage2.htm

PS>You dont need an odd number of cross-overs to get gametes with the mutations in the cis or coupled configuration. This gets complicated but a three or four chromatid strand double cross-over between the area of the linked genes in question does it as well. I couldn't find a picture online of this, but good genetics textbooks (Genetics Hartl 3rd ed. is an example) will have pictures of this.

Check out Joe Compel's site. He has some of the best ghosts around IMO and is a great guy to deal with.