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["Lon J. Rombough" <lonrom@hevanet.com>]

Here's one mechanism.  In a long-lived perennial there will occasionally be cells in which the chromosomes divide, but the cell doesn't split into two, resulting in a new cell that has twice as many chromosomes.  Call this cell a 4x (tetraploid) cell.  If it's in the right place, it multiplies and becomes a new shoot or limb.  When it blooms, it would likely be pollinated with pollen from a normal 2x (diploid).  The result would be 2x x 4x = 3x (triploid).  Now, while a triploid plant is sterile because the odd number of chromosomes mean they don't pair up correctly during meiosis, there is a definite chance of another episode of chromosome doubling in a long-lived perennial, resulting in a shoot on the triploid plant that now has 6x (hexaploid).  The 6x is fertile because each chromosome now has an opposite to pair with.  So the result is a plant with a much higher number of chromosomes.  This kind of thing has happened quite a bit in plants like strawberries and Rubus, and it's the origin of Prunus domestica. 
I know this is probably too short to be terribly clear, but I haven't time to write it all out here.  I'm working  it up for a special project that I'll eventually make available.
-Lon Rombough
Grapes, writing, consulting, my book, The Grape Grower, at http://www.bunchgrapes.com  Winner of the Garden Writers Association "Best Talent in Writing" award for 2003. 
For even more grape lessons, go to  http://www.grapeschool.com
For all other things grape,   http://www.vitisearch.com

On Oct 9, 2007, at 3:52 PM, rob hamilton wrote:

308!?!?!

Alright you geneticist out there explain to me how that occurred!
Did they find the first one at an Uranim mine?  :)

Yeah, I am speaking out the side of my head, but really how could such a vast difference occur with in a species?

Hal Love <lovehd@comcast.net> wrote:Rob,
>  
> Morus nigra is somewhat of a genetic anomaly. It has 308 chromosomes! Morus rubra/alba have 28. I'm not sure any amount of halving or doubling would overcome that much difference (2x vs. 22x).
>  
> Hal
>  
> ********************************************************************************************************************
>  
> "He also told be the Nigra and rubus/alba can not readily cross because of different chromosome count. I would love to dig into that further to see if anyone has tried working with halving or doubling them to make them match."
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