Re: I. sibirica X I. pseudacorus

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The difference is how the chromosomes divide at meiosis.  In amphidiploids the chromosomes do not mix between sets and each gamete (ovules and pollen) get a seperate set of each set of chromosomes of the hybrid parents.  In tetraploids the chromosomes are alike and are free to intermingle and segrates as they please.

Example 1:  I. aphylla x  TB is essentially a tetraploid.  Twelve chromosomes from each parent and are free to mix it up and segregate chatacteristics.  Each gamete will get 24 chromosomes.

Example 2: SDB's are amphidiploids that combine the tetraploid chromosomes of MDB's (32) from pure I. pumila backrounds and the 48 chromosomes of the TB's.  Each gamete will get one set of two sets chromosomes and two sets of twelve for a total of 40 chromosomes. When these plants form gametes the chromosomes divide the set of 16 I. pumila chromosomes into two sets of 8 and divide the 24 TB chromosomes into two sets of twelve. The set of 8 chromosomes pair up and the set of twelve pair up. The cell divides and each gamete will have one set of eight and one set of twelve for a total of 20 chromosomes.

A diploid cross of a diploid MDB such as I. attica has only 16 chromosomes.  Cross that will a diploid MTB or diploid species such as I. pallida and the single set of chromosomes of each set cannot match up completely idf at all withg the other set.  Gametes may form but will not have a complete set or extra chromosomes in an attempt to divde up the genetic material.  Msot times theis makes unbalanced gametes and will create defective seedlings if they mature at all.

Those are not hard and fast rules because sometimes gametes are formed and viable seed is achieved when paired with and appropriate partner.

Beyond that you would need to go back to basic biology to understand mitosis and meiosis and how the chromosomes segregate.

-----Original Message-----
From: gardenersfriend@sasktel.net
Sent: Mar 5, 2011 11:01 PM
To: iris-species@yahoogroups.com
Subject: Re: [iris-species] I. sibirica X I. pseudacorus

 

I almost have to have some models in front of me to really understand ploidy levels in plants. So I may be still a bit hazy on the subject, but here goes my understanding at this point.   Amphiploids are the result of an original diploid (a plant which has two set of chromosomes) to diploid cross between plants which are not closely related such as different species.  Normally these plants would inherit one set of chromosomes from each parent.  Such a âwide crossâ usually results in sterile plants.  However, and here is where I am a little hazy,  Some plants from such a cross instead of inheriting a single set of chromosomes from each parent inherit both sets of chromosomes and these are paired resulting in an amphiploid.  Ok, now at this point I have to ask what is the difference between a tetraploid and and amphiploid?  Are they essentially the same except that we tend to think of tetraploids as generally being the result of genetically related plants and amphiploids being from crosses of initially unrelated plants such as the amphiploid, I. versicolor, which was and is the result of crossing I. virginica and I. setosa.  I guess both are tetraploids, but are of different origins so to speak.?? 

 

From: z*@umich.edu

Sent: Saturday, March 05, 2011 3:45 PM

To: i*@yahoogroups.com

Subject: Re: [iris-species] I. sibirica X I. pseudacorus

 

 

Interesting. Presumably a lot of barriers are selected for to prevent
hybridization in the wild, where sterile offspring are usually dead
ends. I wouldn't be surprised if there's enough variability among
irises that some genotypes might turn out to be compatible among
species that typically can't cross.

Another possibility that occurs to me is that some amiphidiploids
might cross more easily or widely than straight species, if they
express a mixed phenotype say, closer to the average cytoplasmic
makeup for iris.

Sean Z

Quoting "JamieV." <j*@freenet.de>:

> Sean,
>
> I had thought the same, but, apparently the tetraploidy doesn't make
> the plants more compatable that the diploid version, simply allows
> them to reproduce into another generation. Not all genetic barriers
> are understood. It may well be that there are exceptions, but I've
> not found any records of them. One main reason for incompatability
> is the cytoplasm of the seed parent not being compatable with the
> pollen. Regardless of ploidy, a viable embryo is not possible.
>
> Maybe someone with more knowledge in embryo viability can shed some
> more light.
>
> Jamie V.
>
> _______________________
>
> KÃln (Cologne)
> Germany
> Zone 8
>
>
>
>
> Am 05.03.2011 20:10, schrieb Sean A. Zera:
>> I sort of assumed that interspecies crosses between tetraploids would
>> actually be easier to produce. In a diploid cross, enough of the
>> parents' chromosomes have to be sufficiently analogous to pair, or the
>> embryo will be inviable, not just sterile. In a tetraploid cross, this
>> is irrelevant because each chromosome has a compatible twin of its own
>> species to pair with.
>>
>>
>> Sean Z
>>
>>
>>
>> Quoting "JamieV."<j*@freenet.de>:
>>
>>> Jim,
>>>
>>> using tetraploids will give amphidiploid offspring, which will be
>>> fertile. Diploid hybrids often have unbalanced chromosomes and fail
>>> to produce viable gametes during meiosis and are thus infertile.
>>> The advantage lies in the next generations as most diploid
>>> wide-cross hybrids are dead ends. As to whether the actual cross
>>> will be easier to make, I doubt it, but one has a better outcome for
>>> the extra effort to get the cross to take.
>>>
>>> --
>>> Jamie V.
>>>
>>> _______________________
>>>
>>> KÃln (Cologne)
>>> Germany
>>> Zone 8
>>>
>>>
>>>
>>> Am 05.03.2011 00:51, schrieb g*@sasktel.net:
>>>>
>>>> Now this is all very fascinating information for one who likes to
>>>> do some hybridizing! Canât wait to give it a try myself. Also,
>>>> will look forward to seeing this hybrid seedling flower as well.
>>>> I do have a question regarding the use of the tetraploids â why
>>>> would this work any better than using both diploids? Also, it is
>>>> interesting that if siberica and sanguinea are not closely related
>>>> that the offspring from such a cross as still quite fertile??
>>>> Jim in Saskatoon
>>>> *From:* Rodney Barton<mailto:r*@yahoo.com>
>>>> *Sent:* Friday, March 04, 2011 4:12 PM
>>>> *To:* i*@yahoogroups.com<mailto:i*@yahoogroups.com>
>>>> *Subject:* Re: [iris-species] I. sibirica X I. pseudacorus
>>>>
>>>> My understanding is that Siberian Irises, as a class, are mostly I.
>>>> sanguinea. A surprising finding by Dr. Wilson is that I. sanguinea
>>>> is not very closely related to I. sibirica.
>>>>
>>>> Rod
>>>> ----------------------------------------------------------
>>>> *From:* JamieV.<j*@freenet.de>
>>>> *To:* i*@yahoogroups.com
>>>> *Sent:* Fri, March 4, 2011 3:54:21 PM
>>>> *Subject:* Re: [iris-species] I. sibirica X I. pseudacorus
>>>>
>>>> Dennis, et al,
>>>>
>>>> I've tried the cross a few times with no takes, but using
>>>> tetraploids should most certainly work creating an amphidiploid.
>>>> There are quite a few tet sibericas to try. Sultan's Ruby comes to
>>>> mind as being a very reliable garden plant. Dennis, could you send
>>>> over some of the tetraploid pollen? I have SR and a couple of
>>>> other tetraploids in the garden. This may be worth a try.
>>>>
>>>> Jamie
>>>>
>>>> Am 04.03.2011 22:47, schrieb Dennis Kramb:
>>>>
>>>>> I grow both. I can try it this year (if you remind me!).
>>>>> Actually my clone of pseudacorus is tetraploid, so that could
>>>>> improve chances of a successful cross.
>>>>>
>>>>> Dennis in Cincy
>>>>>
>>>>
>>>>
>>>>
>>>>
>>>
>>> --
>>>
>>
>>
>> ------------------------------------
>>
>> Yahoo! Groups Links
>>
>>
>>
>>
>>
>
>
> --
> Jamie V.
>
> _______________________
>
> KÃln (Cologne)
> Germany
> Zone 8
>
>