Re: Re: HYB: spots (was another terminology question)
iris@hort.net
  • Subject: Re: Re: HYB: spots (was another terminology question)
  • From: C* C* <i*@aim.com>
  • Date: Wed, 27 Feb 2013 11:35:37 -0500 (EST)
There are many , many situations where strange plants can produce seed. Such as the ditch dayliily, Hemerocallis europa, a triploid. Basically sterile, but can produce seed in rare crosses. A very low number. My Eternal Summer a 12/2/2/8 hybrid, won't set seed with the pollen I put on it, but there is a seed pod on about 1 out of 100 flowers, and each with10-30 seeds.And the 12 chromosome sets are two aphylla sets of 12, one TB set of 12, and one pumilla set of 8.
For the triploid banana (Cavendish) which is the basic store banana, has 3 x33 chromosomes. Calculation for fertile gametes is 1/2 to power of 11. This is the sort of thing you get with unbalanced chromosomes. So the answer, is very reduced fertility. By a huge factor.
We have always had some, very limited fertility in IB plants, which is consistent with their ploidy. The sudden increase in fertility currently seen in IB is something I can't explain, and doesn't seem to fit the 12/12/12/8 composition. To get IB X IB is one step higher on improbability scale. Actually several huge steps up on improbability scale. I'm very suspicious that an analysis of fertile IB will show an amphidiploid structure.
I spoke with a genetics professor at U of Guelph this morning. He agreed that the amphidiploid explanation is the most feasible, and couldn't think of any other explanation. He is going to think about it more and get back to me. I'll be asking a couple of the other professors as well.
If there are four homologues (matched chromosomes) between the 8 set and 12 set, this may be helping, but the problem still arises with the uniploid chromosomes (unmatched).
In an IB with 12/12/12/8, it is probably more likely for the three sets of 12 to form tri-valents. And the 8 set to form univalents. Actually this would increase the number of viable gametes. Calculations would be (1/2) to power of 2 times(1/2) to power of 8. A pretty low probability, but with so many pollen grains, you will occasionally get lucky.
In terms of cross overs, also consider that the pumilla 8 chromosome set has only two plicata genes. The non plicata, and the glaciata. No regular pl gene ,and no luminata gene. And in all the years of breeding, there hasn't been a cross over on this, as well as none on pumilla spot. So basically, if it could have happened, it would have happened by now. 

Chuck Chapman

-----Original Message-----
From: Linda Mann <lmann@lock-net.com>
To: iris <iris@hort.net>
Sent: Wed, Feb 27, 2013 6:04 am
Subject: Re: [iris] Re: HYB: spots (was another terminology question)

Thanks for the details, Chuck.

The impression I got from that old article is that all the modern
bearded irises are "closely" related (including the ones with different
base n numbers of chromosomes) such that there can be enough of the kind 
of pairing you describe to get viable embryos occasionally.  Not often,
but not never.

It's not like crossing horses and donkeys, although even with equines,
there have apparently been two examples of crossovers there as well,
where a mule produced not a mule, donkey, or horse offspring, but a
genetically mixed offspring.
I can tell it's winter and we are all impatient for spring, to be having 
these esoteric, theoretical discussions.

---------------------------------------------------------------------
To sign-off this list, send email to majordomo@hort.net with the
message text UNSUBSCRIBE IRIS

---------------------------------------------------------------------
To sign-off this list, send email to majordomo@hort.net with the
message text UNSUBSCRIBE IRIS
Other Mailing lists | Author Index | Date Index | Subject Index | Thread Index