Re: Re: Iris abicans

I have Simonet's paper in from of me. In his examination of albicans he found 16 bivalent chromosomes and 12 univalent ( unpaired ) chromosomes.  While your explination could fit for 44 chromosomes we still have the one set of 12 that is unmatched. I'm not sure how to account for 16 paired chromosomes. If two sets of 8 paired, then this would be an unbalanced pentaploid. 
Perhaps someone else could look over this document and comment.

Chuck Chapman

"David Ferguson" <manzano57@msn.com> wrote:

>To expound on this a bit.  The 44 chromosome Iris are technically unbalanced tetraploids.  They have a make up of 8 + 12 + 12 + 12 chromosomes.  They come from a 40 chromosome parent crossed with a 48 chromosome parent (or as Sharon stated, perhaps an unreduced gamete from a 24 chromosome parent).  The 40 chromosome parent is an amphidiploid (also technically a tetraploid, not unbalanced, but with two sets of 8 and two sets of 12 chromosomes - so fully fertile - functionally diploid with two matched sets of 20), and these are derived from a cross of a 32 chromosome parent (or unreduced 16) with a 48 chromosome (or unreduced 24).  So, the plants end up with three sets of 12, and one set of 8.  In the old "wild" 44 chromosome types such as albicans the sets of 12 could all be from one parent species, or from two.  The set of 8 is most likely from I. pumila in all cases, but if from an unreduced gamete could be from one of the 16 chromosome species (it had to contribute 16 to the 40 chromosome parent - only 8 of which make it into the 44 chromosome plants).
>
>Anyway, the set of 8 chromosomes doesn't sort nor pair up properly with the sets of 12 during meiosis, and this is probably the main reason for reduced fertility.  The odds are against success, but obviously success occurs occasionally, as there are several cases where 44 chromosome plants have produced offspring.  The offspring can vary in chromosome number, depending on how the chromosomes sort into the gametes during meiosis, and depending upon what the "other" parent is.
>
>To me it seems most likely that the "wild" ones (albicans, germanica, florentina, etc.) are derived from Near Eastern tetraploids crossed with I. pumila, but these aren't the only possibilities.  The tetraploids were apparently cultivated and carried around by people, or at least this seems the most likely explanation to why they have popped up as "wild" populations here and there (not commonly) up all the way to the west end of the Mediterranean.  These crosses must have been rare, since the wild TB Iris flower so much later than the dwarfs.  Once established though, they seem to have been very successful at surviving.  Seems the 44 chromosome hybrids were more successful as cultivars and at naturalizing than their parent, since they are widespread and common.
>
>The wild parentage thing is all supposition on my part.
>
>
>
>Dave
>  ----- Original Message -----
>  From: arilbredbreeder@cs.com<a*@cs.com>
>  To: iris-species@yahoogroups.com<i*@yahoogroups.com>
>  Cc: smciris@aol.com<s*@aol.com>
>  Sent: Friday, March 25, 2005 10:00 AM
>  Subject: Re: [iris-species] Re: Iris abicans
>
>
>  irischapman@netscape.net<i*@netscape.net> wrote:
>
>  >
>  >My understanding is that Albicans is a triploid(Simmott) and that triploid pollen is even less fertile then egg cells. The triploidy is apparently what restricts the fertility. I would think self pollination would be near impossible.
>  >
>  >Has anyone observed bees actually visiting albicans flowers?
>  >
>  >Chuck Chapman
>
>  According to both Simonet & Randolph it has 44 chromosomes.  There are a number of 40-chromosome and 48-chromosome species in the area that are good candidates for its parental species.  Or an unreduced gamete of one of the 24-chromosome species could have been involved.  Many amphidiploids are self-sterile [beyond the scope of this discussion] but prove fertile with other clones of the same type.  The catch, in this case, is that I. albicans has been vegetatively propagated for so long that there appears to be a very limited gene pool.
>
>  Sharon McAllister
>
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