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Re: yellow inheritance


Ben wrote:
>It is much simpler: green is always gg and yellow leaf is Yg

to which halinar@open.org responded:
RE:>>Don't you mean that green is yy and yellow is Yy? What is Yg?

To which I pose the following;
From what I can tell of this conversation, and my stumblings around into molecular bio, it seems to me that the equation is a bit more complicated than Yy or Yg.   Maybe it was gg and Yg on one set of alleles, but gg and Yb on another, and gw and Yw on another (respectively, pod and pollen parents).  Now 50% of the progeny would be Yellow and nuclear, but not because of a single gene.    Of course, leave it to me to take what is simple and make it complex, but consider this.   What I'm asking is, "how many genes are involved in coloration of Hosta"?

Drosophila Melanogaster has three genes involved with the trait of red eye color.  The trait for red-eye color is carried on Chromosome 1that also happens to carry the gene for control of gender (X-Linked, I believe).  Crossing over in meiosis is not a rare event.  In humans, and most other eukaryotic species, meiosis cannot even be completed properly unless each pair of homologous chromosomes takes part in at least one crossover  (Biology, Starr & Taggart 1998, pg. 200).  The more distant the gene from the centromere, the higher the probability that a crossover will disrupt the linkage (ibid, pg. 201).   The crossover in Drosophila is so pronounced that in the F1 cross between a white-eyed, mininiature-winged female with a red-eyed, normal winged (wild) male, 50% of the offspring switch genotype with the gender intact (or you could look at it the other way).  In the F2 generation, 36.9% were recombinants on at least one of the traits.  The genes were swapped on the chromosome for sex in F1, but 36.9% switch back on two of these traits in the F2 generation (ibid, pg 200).  (Original work of Thomas Hunt Morgan).

If this occurs in meiosis in Drosophila, it seems likely that it occurs in meiosis in Hosta.  The question I need to better understand is how likely is it that this crossing over occurs in MITOSIS, as well as meiosis, which eventually leads to sports.  (I just read Ben's article in AHS HJ, Vol 30. No. 1, pgs. 56-58), and while I could agree with Ben that mit rec is one very likely explanation of the origin of sports (as is crossing over in meiosis THE explanation for genetic changes, leading to plastid changes that lead to new phenotypes, both stable and unstable), I have some questions that need to be resolved regarding this statement that ALL Yellow progeny from a cross of a Yellow Cultivar with a Green Cultivar would be due exclusively to nuclear DNA changes as a direct result of the cross with the Yellow pollen parent.

What percentage of the progeny would have been Yellow if the pod parent had been selfed?  Was there a control in this experiment?  Do you state this in an article and I've simply missed the reference?  If so, please let me know.  

BTW, would mitotic recombination in the meristematic tissues potentially INCREASE if one adds more water and sunlight during the early spring (or would this be more likely to simply affect those plants that are more subject to Chimeral Rearrangement).    Could one increase the appearance of sports simply by manipulating the variables of water and UV radiation?

Also, I believe that Jim Wilkins article (HJ, V30, No1, Pg 58) which follows Ben's is pointing out that there is good cause to believe that coloration in Hosta is controlled by mulitple genes.  I am wondering about BZ's statement that "all sports that are due to chimeral rearrangement are identical".  A phenotypically and significantly different plant but it is genetically identical?  I'd like to see base-pair sequencing or geneome mapping that would back up this statement, Ben.  Can you point me to some research?  :-)

P.S.  Has anyone begun the process of sequencing and isolating genes that influence coloration in Hosta?  Maybe Ben Lockhart or Frank Riehl?  

P.S.S.  My next question Ben may be about linkage mapping as a means to better understand sporting.  I probably have to sign up for a class and send you money before you'll venture into that discussion.  :-)

-- 
Andrew Lietzow
#1 Plantsman at http://hostahaven.com
1250 41st St
Des Moines, IA 50311-2516
 



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