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Re: HYB: tetraploid - long, technical, and probably over the edge

  • To: Iris-talk <iris-talk@onelist.com>
  • Subject: Re: HYB: tetraploid - long, technical, and probably over the edge
  • From: Linda Mann <lmann@icx.net>
  • Date: Fri, 16 Apr 1999 07:39:09 -0700
  • References: <924247973.32415@onelist.com>

From: Linda Mann <lmann@icx.net>

Vicki Craig wrote:
> Pumila, the small iris which were crossed with the
> tall bearded iris to produce standard dwarf bearded iris have two sets
> of 8 chromosomes or 8-8-8-8. That makes pumila a tetraploid. Modern tall
> bearded (those big beautiful things one sees in most all TB catalogs)are
> also tetraploids having 2 sets of 12 chromosomes. i.e. 12-12-12-12. when
> these two tetraploids are crossed they can produce an iris which has two
> sets of chromosomes 8-8-12-12.

Now to try to throw in a Linda Mann wacko idea here - one of the things
I've been wondering about for some time is the 50 chromosome crosses
that were so important in starting the tetraploid TBs.  These were
(perhaps) crosses of tetraploid "tender" 12-12-12-12 TB's with
?unreduced diploid "tough" 12-12's.  I assume this is written with 12 as
the largest common denominator.  But maybe for purposes of this wild
idea, we could consider each 12 to be 3 sets of 4 [i.e., 3(4)] or even 6
sets of 2 [i.e., 6(2)].  
50 to 52 chromosomes seems to have been a common result in early
development of tet TBs (see HIPS page) which implies to me that some of
these sets don't match up right.  It's easier to imagine getting 52
chromosomes from 3(4)-3(4)-3(4)-3(4) in both parents where 1 of the sets
of 4 from each parent don't match up: 1(4)-1(4)-2(4)-3(4)-3(4)-3(4)
where there are two mismatched 1(4)'s, one from each parent
(4+4+8+12+12+12=52). 

Or getting 50 from 6(2)-6(2)-6(2)-6(2) with 1 set not matching:
1(2)-1(2)-5(2)-6(2)-6(2)-6(2) or 2+2+10+12+12+12=50.

Then, in both cases, subsequent generations, one of the extra un-matched
sets gets dropped resulting in stable tets of 48 chromosomes.

Since different 50 chromosome 'tets' seem to have resulted in very
different weather tolerances amongst descendants, my wild thought is
that  ==========
which of those extra sets gets dropped might have a strong influence on
growth characteristics.
==================

Last winter, Jeff Walters and I were offlist tracking maternal pedigrees
trying to make some sense of what we were finding when so much wound up
back with the supposedly 'tender' mediterranean tetraploid species & now
Mike Lowe confirms from personal experience that these mediterranean do
indeed croak after sudden spring or continuous winter nasty cold.

Then there is AMAS...

Linda Mann east Tennessee USA
no shredded petals here, no hail, gusty regular winds yesterday, ~38oF
this am.  The weekend may prove to be more interesting than I would
like.


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