Re: yellow inheritance

Andrew:

>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).

I'm having a very hard time trying to figure out what it is you are 
trying to say, as have some others who sent private emails to me.  It 
is clear that you do not have a good grasp of Mendelian genetics.  And 
it seems from Ben's response that he either made some serious 
typographical errors or he also needs a refreasher course in Mendelian 
genetics.  Bob Axmer has posted some of my Genetics 101 messages on 
his web site.  Don't know the URL off hand, maybe Bob can send it to 
you.  If you go to google.com and type in genetics 101 you will find 
it fairly easily.  I think it should provide you with some basic 
information. It was written for a daylily group, but the basic 
information is the same.

Every gene has a certain location on a chromosome called a locus and 
in a diploid there are two copies of each gene, one from the pod 
parent and one from the pollen parent.  Each gene is given a symbol, 
such as Y or H or Pa or Chr-1.  Genes come in different flavors called 
alleles.  In the case of yellow leaves in hostas there is a "yellow 
leaf" gene that is given the synbol "Y" where Y is the dominant gene 
that causes yellow leaves.  There ia a non active allele of this gene 
called y that does not function, hence it does not produce yellow 
leaves.  There could also be other alleles of the "yellow leaf" gene 
that are only partly functional.  These allels could be called y-1, 
y-2, etc (actually, the number would be a subscript, but I can't write 
a subscript in ASCII email.  These alleles differ in their base pair 
arrangment so that they produce a enzyme that has a different amino 
acid at a certain location.  That different amino acid may not have 
any effect on the functioning of the enzyme, or it could totally shut 
down the enzyme.  It could also make the enyzme function at a much 
slower rate.  Thus, for every gene at a certain locus there are many 
different possible alleles, but a diploid can only contain two alleles 
of each gene, one from the pod parent and one from the pollen parent.

Now, a hosta is either YY, Yy or yy, if we are talking about a fully 
functional gene and a totally nonfunctional gene.  Other hostas could 
be (y-1 y) or (y-1 y-2) or (Y y-1) or how ever many different 
combinations that can be made from the total number of alleles taken 
two at a time.

I don't know what your proposed G or green leaf gene is.  The 
biosynthesis of chlorophyll is VERY complex and there are probably a 
hundred or more genes involved in chlorophyll synthesis.  A mutation 
in any one of these genes could result in the failure of the plant to 
produce chlorophyll if it occures in the early to mid part of the 
biosynthesis, while it can result in a yellow pigmment that is close 
to a fully formed chlorophyll molecule, but not quite complete, if the 
mutation is in a gene at the end of the process.  These late forms of 
chlorophyll are generally yellow pigments.  

The yellow leafed gene "Y" is probably an inhibitor gene that somehow 
stops chlorophyll synthesis before it is completed.  The reason that 
many yellow leafed hostas "green up" during the year is that inhibitor 
genes are often temperature sensitive.  The "Y" gene is not in the 
chlorophyll biosynthetic pathway.  Now, there could be a mutation in 
the chlorophyll biosynthetic pathway that stops chlorophyll synthesis 
and we could call this gene Ch.  We could also call it "a" for albino, 
or "w" for white.  Now, for a hosta to produce "green leves", that is, 
leaves with chlorophyll, it would have to be genotype ChCh yy or Chch 
yy, which can also be written Ch__ yy where the "_" underscore can be 
either CH or ch.  The Ch and Y genes are two completely different 
genes at different locations on the chromosomes.  They could be on the 
same chromosome or different chromosomes.  A hosta with genotype chch 
yy would be albino and a genoype of chch Yy would also be albino 
because the ch gene stops chlorophyll synthesis before the Y gene can 
do it's dirty work.  

Joe Halinar

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