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Re: Yellow leaves

  • Subject: Re: Yellow leaves
  • From: halinar@open.org
  • Date: Sat, 15 Feb 2003 13:50:34 -0800 (PST)


>So a hosta can never have a hidden yellow gene.

You need to reconsider some basic Mendelian genetics along with some 
polyploid genetics.  Dominant genes can easily be made to look like 
recessive genes and vice versa, and with amphidiploids its very easy 
to have fixed heterozygosity.  

First of all, you have never said if you believe if the yellow gene is 
an inhibitor gene acting to block chlorophyll biosynthesis or if it is 
an allele of a gene within the chlorophyll biosynthetic pathway.

If you have a gene "G" for green leaves and an inhibitor gene "I", 
then the geneotype GGIi will make yellow leaves look like a dominant 
gene when in fact green leaves are dominant but it is the domiant 
inhibitor gene that you are really seeing.  

If you have a yellow allele for an otherwise green gene, you would 
expect that to show up as a recessive allele since it would be 
blocking chlorophyll biosynthesis, for example, GG and Gg would be 
green and gg would be yellow.  In this case it would also be easy to 
hide the gg genotype in a fixed heterozygous condition because of the 
amphidiploid nature of hostas -  GG on one genome and gg on the second 
genome.  A rare homeologous cross over could eventually bring out the 
recessive genotype.

Make the active gene a dominant complimentary gene and the inhibitor 
gene a dominant complimentary gene and you can come up with some 
really interesting cases.  

Joe Halinar

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