re: Re:Auto-tetraploid versus amphidiploid was Hyb spots
iris@hort.net
  • Subject: re: Re:Auto-tetraploid versus amphidiploid was Hyb spots
  • From: C* C* <i*@aim.com>
  • Date: Sun, 3 Mar 2013 09:05:40 -0500 (EST)
One thing I find fascinating with Randolph's work is his patience and ability to sort out the chromosomes. He was using at pollen, to try and catch it in exactly the right stage of meiosis. Namely a certain stage of Meiosis I, just before first division, exactly when the duplicated chromosomes were lining up at the cell division plate. The cells were killed with alcohol, then he searched through his slide , until he found a cell in the right (or nearly right, as you can see in his photographs) and then had to sort these cells all out, even if they were piled up on each other. And he did this all at around 800-1100 X. Now light microscopes can go up to 2000 x resolution, but this requires using an oil immersion lens. Now if anyone who has used a scientific light microscope knows, this is a time consuming process. As each time you change slides you need to clean lens, and reapply the oil. Randolph , to do this study, looked at several hundred slides. He looked at 30 cultivars, and up to 72 slides on at least one. This doesn't include the slides that didn't show anything. I assure you that there were a number of those as well.
Now to put his procedure into further context. This was pretty much the standard procedure used up until early 1950's. Using this procedure, the human chromosome was identified as having 48 chromosomes. And this was with 100's of researchers looking at slides. So a procedure that had some limitations. In early 1950's a new procedure for looking at cells in mitosis, or meiosis was developed. (Cells have to be looked at at time of division, as they are condensed into chromosome structures at this time, and only at this time. the rest of the time they are rather diffuse blobs, and you can tell one from the other) By using colchicine, cells are arrested at exactly the right time for a good observation. Just after lining up at mid point, and the chemical prevents separation of chromosomes. That is also why it works on doubling chromosomes in plants and producing tetraploids from diploids. Then chromosomes are further separated for good viewing using a salt bath. when this procedure was used, lo and behold, it turned out humans had 46 chromosomes, not 48 . A better method, better observations.
So bottom line, some of the tetrads may have been paired bivalents rather then tetravalents.
As a last note for this post, the statement "Thus, in tall bearded hybridizing it is possible that any allele can eventually be recovered as a tetraploid homozygote with four doses." is Kidd's interpretation of Randolph's research, not what Randolph said. I suspect Randolph would have disagreed with that interpretation. He had already done the study showing that tetravalents contributed to lower fertility. 

Chuck Chapman







-----Original Message-----
From: Tom Waters <irises@telp.com>
To: iris <iris@hort.net>
Sent: Fri, Mar 1, 2013 6:45 pm
Subject: re: [iris] Re:Auto-tetraploid versus amphidiploid was Hyb spots

From _The World of Irises_ (p.392):
"Heinig and Randolph (1963) studied the meiotic behavior of tetraploid iris species and tall bearded varieties. Their observations indicate that for many and possibly most chromosomes tetrasomic pairing can occur, even among the technically allotetraploid cultivars. However, in any one variety not 
all chromosomes showed such pairing and the number that formed
quadrivalents varied among the cultivars studied. Nevertheless, enough
homology exists among the n=12 genomes to allow occasional allosynapsis
(the pairing of chromosomes from different species). Thus, in tall bearded hybridizing it is possible that any allele can eventually be recovered as a 
tetraploid homozygote with four doses."




Tom Waters


Telperion Oasis ~ www.telp.com/irises


Cuyamungue, New Mexico, USA (zone 6)

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