Hi El! I have an article on my website which may or may not be
helpful:
http://www.telp.com/irises/chromosomes.htm
The
examples I use are for bearded and aril irises, but the basic principles are the
same for any types.
All the information about chromosome numbers
sometimes obscures the basic ideas. The total number of chromosomes an iris has
is important in that it gives information about
(1) the number of
chromosome sets (2=diploid, 4=tetraploid) and
(2) the number of
chromosomes in each set, which can cast light on whether the chromosomes of two
different irises are compatible enough to pair.
For an iris to reproduce,
each chromosome set needs another compatible set to pair with. For a diploid,
this means both sets compatible; for a tetraploid it means all four sets
compatible or else two pairs of compatible sets.
It's a lot like sorting
socks. :)
Tom
--- In i*@yahoogroups.com,
Eleanor Hutchison <eleanore@...> wrote:
>
> Thank you,
Anner.
>
> I was looking for a simple explanation of the relevance
of the chromosome count, as they seemed rather out of whack in some cases. That
part seems a little clearer now. I still also plan on checking some crosses that
have been successfully done with some of the iris I have.
>
> These
books sound very interesting, and I'll hunt them down.
>
> All
lovely ways to wile away the long winter days up here.
>
> El, Ste
Anne, Manitoba, Canada
>
>
> From: ChatOWhitehall@...
> Sent: Sunday, January 02, 2011 6:05 PM
> To: i*@yahoogroups.com
> Subject: Re: [iris-species] Chromosome Count
>
>
>
>
> Good evening, El.
>
> I'm not sure what you are
looking for, exactly, and this is not the sort of thing I know a lot about,
frankly, but if you are wondering what will cross with what, and how that
happens, then some information on what has been crossed successfully with what
may be useful.
>
> Appendix C of the book Garden Irises, published
by the AIS in 1959, edited by Dr. L. F. Randolph, Is entitled "Check List of
Iris Species Hybrids", and, while dated as to what species are included, is
pretty comprehensive. It has been said by people who appreciate these things
that Garden Irises is the most scientific of the several books published by the
AIS. If you go to one of the various book search facilities on the web--I use
AddAll.com where I select the used book option-- you can find a copy for not
much money. Appendix D of the selfsame book is a listing of chromosome counts of
Iris species. Chapter 22 is entitled "The Chromosomes of Iris Species," and it
was written by Dr. Randolph and his student, Jyotirmay Mitra. Dr. Randolph was
President of the AIS and a professor at Cornell.
>
> Otherwise, the
earliest fertility--or sterility--studies reported by the AIS are those
undertaken by Dr. A. B. Stout and his students at the New York Botanical Garden,
published in several AIS Bulletins in the interwar years, notably July, 1925;
Oct. 1926; Jan. 1927; April, 1928, and in September, 1937, the latter, according
to the title, being a discussion of Ii. versicolor and laevigata, and the LA
irises. This is the same Dr. Stout who was involved with Hemerocallis.
>
> I hope this is helpful.
>
> AMW
>
>
>
>
> -----Original Message-----
> From: Eleanor Hutchison
<eleanore@...>
> To: i*@yahoogroups.com
>
Sent: Sun, Jan 2, 2011 6:14 pm
> Subject: Re: [iris-species] Chromosome
Count
>
>
>
> All I wanted was a simple explanation,
so I thank you, Dave!
>
> I may end up checking out what crosses
were already successful, and give a couple a try.
>
> El, Ste
Anne, Manitoba, Canada
>
>
> From: David Ferguson
>
Sent: Sunday, January 02, 2011 4:26 PM
> To: iris-species
>
Subject: RE: [iris-species] Chromosome Count
>
>
>
>
Here is a very marginal answer. Somebody else here can probably get more
specific.
>
>
> Even if the chromosomes are different in
number, if the species are closely related enough, they may hybridize with
little difficulty. Usually the species with the larger number has the same basic
chromosomes, little different from the one with fewer, it just has more of them.
Sometimes the ones with more are simple polyploids, having multiples of the
exact same chromosomes. Sometimes there are supernumerary chromosomes, which are
usually extra copies of one or more of individual chromosomes, or which may
represent a chromosome that split into two. Sometimes most or all of two
chromosomes might fuse together into one, to make a lesser total number.
Sometimes the numbers are shifted due to crossing of species that have different
base numbers that become combined into a new larger full set (these may include
duplicates, but they behave as if different). Regardless of why the numbers
differ, if the chromosomes match up well enough, a plant can result from
crossing two related species, regardless of chromosome numbers. Sometimes though
the chromosomes are different enough, or enough errors occur in pairings, that
some or all attempts at a given cross will fail. Sometimes supernumeraries will
join up with like ones to make three-somes, sometimes the extras just hang
around and don't pair up. I don't know all the details of what happens with
Iris, but they should follow the same rules as most any other plants.
>
>
> The next part of the question is "are the hybrids fertile". If
there are enough discrepancies in the chromosome pairings, or if there are other
incompatibilities, they may be unable to produce offspring, and end up being
basically genetic dead ends; or, at least the successes will be few and far
between. Sometimes if you can double the hybrid's number (if you can get
unreduced gametes), you can restore fertility with others that have like sets of
chromosomes (or when the hybrids are self-pollinated).
>
>
>
Sometimes in higher ploidies, there are so many copies of the same chromosome,
that the numbers start to become almost irrelevant, as long as some full sets
are represented in gametes, and can pair up when fertilized. (In some groups of
plants having just full sets seems to be more important to fertility than it is
in other groups of plants).
>
>
> It can get pretty
complicated when all the ramifications and combinations are considered, but
maybe this is enough to help a bit.
>
>
> I need to learn
more about chromosomes specifically as they occur in Beardless Iris before I
could elaborate more. I'm not even sure what the base haploid number is for
"water Irises", nor whether some of them have fused chromosomes or
supernumeraries in their compliments. It appears that the ones you listed have
very unrelated numbers, but when broken down more, they probably would make more
sense.
>
>
> Dave Ferguson
> in New Mexico
>
>
>
----------------------------------------------------------
> To: i*@yahoogroups.com
>
From: eleanore@...
> Date: Sat, 1 Jan 2011 14:17:35 -0600
> Subject:
[iris-species] Chromosome Count
>
>
>
>
> Can
someone please give me a simple explanation on hybridizing, using the chromosome
count.
>
> For example, I was just checking I. versicolor on SIGNA,
where it mentions the chromosome count is 2n=108. It easily crosses with the
laevigatae series, which has a chromosome count of 2n=32, while I. virginica has
2n=70 or 2n=72, as does I. virginica var shrevei.
>
> Thank
you!
>
> El
>
