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: Thu, 28 Feb 2013 13:12:13 -0500 (EST)
That fits well. As the only way to get lower seed count of aphylla MTB X SDB would be if the MTB was an amphidiploid. 

Chuck Chapman

-----Original Message-----
From: Bill Chaney <billchaney@ymail.com>
To: iris <iris@hort.net>
Sent: Thu, Feb 28, 2013 12:45 pm
Subject: Re: [iris] Re:Auto-tetraploid versus amphidiploid was Hyb spots
I have been doing a LOT of aphylla bred MTB X TB crossing (using the tet MTBs from the Craigs, Hager or Fisher). I have also been doing some aphylla bred MTB X SDB and aphylla bred MTB X IB. One observation from my work and also from Vicki Craig, is that seed counts and germination of the crosses with the SDBs and IBs is lower than with the TBs, but germination will improve if you hold seed pots for a second year. I also see this with diploid X Tetraploid 
crosses.  The aphylla bred MTB X TB crosses produce seed counts and
germination rates equal to TB X TB for me.

Bill Chaney
________________________________
From: Chuck Chapman <irischapman@aim.com>
To: iris@hort.net
Sent: Thursday, February 28, 2013 8:46 AM
Subject: [iris]
Re:Auto-tetraploid versus amphidiploid was Hyb spots

We had been discussing
aphylla  X TB hybrids and fertility.

Actually, it turns out that full
tetraploids, (autotetraploids) with four identical genes, have much reduced 
fertility compared to amphidiploids, or straight diploids.

This is because
during meiosis (forming of gametes, eggs and pollen) four sets of identical genes often form tetravalents. And during first stage of meiosis, either all of these four genes go into one cell, or the other, leaving no copies in the other cell. When there is small differences in the four sets of genes, of a particular chromosome, you get two bivalents and so proper division during 
meiosis

Now remember,  most tetraploid iris, at least the TB iris , have
multiple species involved in their creation, so probably a number of genes 
from different species, with enough of a difference, and enough of a
similarity, to pair up as fertile bivalents , rather then tetravalents during 
meiosis.

Also almost all ( I'd say all, but there probably an exception or
several out there somewhere) fertile tetraploids found in nature, are a result 
of an inter  species hybrids, and thus are  amphidiploids, rather then
autotetraploids.

So fertile 4x 48  iris are should basically be considered
amphidiploids. The infertile ones are probably autotetraploids.

Look up
"fertility in autotetraploids"

Chuck Chapman
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