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Re: Deadlyish nightshades (was Re: A Potato Question)

Bill DeWitt wrote:
> 
> At 07:42 AM 8/12/98 -0700, you wrote:
> >If no one wants the fruits of their potato plants, I'd be glad to take
> >them for the seed they contain.  I've grown potato seedlings before and
> >while most of them are worthless, they are a fascinating experiment in
> >how much a given progeny can vary.  Remember, Luther Burbank selected
> >the Russet Burbank potato from a small group of seedlings of Early Rose
> >potato.  I've gotten some that were different enough to be worth growing
> >as ornamentals.
> 
>         So, what I am wondering now is... do the seeds of potatoes grown from seed
> vary as widely as the seeds of potatoes grown from tubers?
>         Since I am guessing that the variation comes from the fact that the potato
> tuber is a direct clone of a hybrid, and the seed is not, then I am also
> guessing that the second generation would not vary as much, if at all.
>         But if I am right, where are all the direct seeded varieties of potato?

Most cultivated potatoes are polyploids, having more than one set of 
chromosomes, which means that there is a lot more genetic variation in 
them than you would expect.  Seedlings of a seedling will still vary a 
lot.  Think of it this way.  If a plant with one set of chromosomes has 
the configuration Aa for a single gene and you self-pollinate it, you 
can get three kinds of offspring - AA, Aa, and aa.  (A being one form of 
the gene and a being the other form, so that AA is red flowers, Aa is 
pink, and aa is white flowers, for example) But if it has more than one 
set of the same gene,  AAaa, the self-pollination of that plant gives 
offspring that are AAAA, AAAa, AAaa, Aaaa, and aaaa.  If the plant has 
*THREE* sets of chromosomes... well, you get the idea.  And that's for 
ONE gene.  When you put all the thousands of genes together, you can see 
that it could take quite a few generations of self-pollinating and 
selecting to get seedlings that would come even close to being true to 
the parent.
Clear as mud?
-Lon Rombough
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