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nafex - Re: [NAFEX] Morus nigra in North Carolina

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  • From: "Lon J. Rombough" <lonrom@hevanet.com>
  • To: North American Fruit Explorers <nafex@lists.ibiblio.org>
  • Subject: Re: [NAFEX] Morus nigra in North Carolina
  • Date: Tue, 9 Oct 2007 18:20:05 -0700

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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