HYB: Tetraploids
From: Sharon McAllister <73372.1745@compuserve.com>
Message text written by Vicki Craig:
>
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.
<
Excellent example.
> These are not tetraploids. they are
called an amphi-diploid. Somehow the mistaken notion of if you cross
two tetraploids of any count the results will be another tetraploid. Not
true.
Hope this helps clear this subject up. And yes even hybridizers who are
unfamiliar with the genetic make-up of different iris can err in their
terminology. Based on the background of Blue Chip Stock and without a
chromosome count I would place my money on it not being a tetraploid.
<
Vicki -- at the detailed level of chromosome conjugation, I certainly agree
with you about the importance of distinguishing amphidiploids from
tetraploids. The problem is that some people go no further than the
elementary definition of "having four sets of chromosomes". This not only
leads to considering any amphidiploid to be a type of tetraploid, but also
classifies the progeny of a cross of two different types of tetraploids,
such as a tetraploid dwarf and tetraploid TB you cited, as tetraploids
simply because they normally do have four sets of chromosomes. Not four
sets of matching, or homologous, chromosomes. Not necessarily even a
functional tetraploid. Just something with four sets of chromosomes,
however ill-matched.
Lurkers -- please note that Vicki and I can understand each other even
though we tend to use different terminology. Most of us adopt the
terminology used by our mentors, and that's not always the same in all
parts of the world of iris. In my case, when I turned serious about
hybridizing I had better access to academic journals on plant breeding and
genetics than to iris publications so I tend to use many of their terms.
I think this underscores the importance of knowing not only what we mean by
certain terms ourselves, but also how others have used them.
As for Blue Chip Stock, I'd certainly bet against it being an
autotetraploid but don't know enough about it to lay odds as to its being
an aneuploid rather than an unbalanced allotetraploid.
Anyone for a Hybridizing 301 assignment of charting the possibilities? <G>
Sharon McAllister
73372.1745@compuserve.com
------------------------------------------------------------------------
Share the wealth!
http://www.ONElist.com
Tell a friend about ONElist's 115,000 free e-mail communities!
