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white petunias

Mary (as "Darren Briner" <dmjb143@brigadoon.com>),
Yesterday,  you asked:
> I took seeds from several petunia plants of different colors last year
> and this year they are all blooming white. Does anyone know why that is?
> I think the original plants were pinks and purples.
I assume that you purchased the petunias from which you saved seed at a
garden center last season.

My guess is that there were white petunias somewhere nearby.  There are 
apparently dominant genes for white in the material from which you saved 
seed, so that (white x any other color) gives you seed which produces 
plants which have white flowers.  Seed from those white-flowered plants 
should throw some colored-flowered plants, but most will still be white.

Although most introductory genetics texts only describe white as a bottom
recessive (i.e., every other color allele possible is dominant to white),
the white-as-top-dominant example also happens all of the time.  It's a
biochemical thing: the earlier in the biosynthesis of color that a gene
takes action, the more likely it is to effect everything "downstream".  

This would not be true if many of the plants were producing colored
flowers.

Rick Grazzini
rickg@centrelab.com
USDA 6 / Sunset 43
central PA --- where the blue-and-white flowers of the Nittany Lions have
begun to bloom ...
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