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  What is Aneuploidy?
From: ted.held at us.henkel.com (ted.held at us.henkel.com) on 2008.01.07 at 10:01:38(16930)
Dear List,

I have managed to finish the latest Aroideana. It's probably a good thing
for me this comes out only once a year as it seems like it takes me a year
to read and digest what's in one. Being a lay person, some of the articles
can be heavy-going. The one entitled "The Chromosome Numbers of the Aroid
Genera", by Dr. Bogner, is a case in point. I am trying to sort out what
the apparent promiscuity of aroids with regard to chromosome numbers might
mean. Here are some questions?

1. Do all the plants within a given species have the same basic "X" number
of chromosomes? Does this mean a species within the genus Landoltia, for
example, might have a normal 2n chromosome count of 40 with haploid (2n =
20), diploid (2n = 80), etc., variations, but not 2n = 46? So if you have
two plants, one with 2n = 40 and another with 2n = 46, do you know you
have two different species?
2. Can plants with different chromosome counts be cross fertile? Can a 2n
= 40 plant produce viable seed with its own diploid? How about with a
plant in the same genus with a chromosome count of 2n = 46?
3. What happens when a plant messes up and undergoes aneuploidy.
Aneuploidy is defined in the text as when some type of evolution takes
place where the offspring end up with a few extra chromosomes here and
there. Doesn't this mess up the plant? If not, why not?
4. Similarly, there is a term called dysploidy where a few chromosomes
don't make it into the new plants, or where old chromosomes get pieces
chewed off, somehow. Don't plants need at least a portion of the
information contained in the chromosome arms? Doesn't this mess up the
plant? If not, why not?
5. Can a plant that has experienced aneuploidy or dysploidy produce viable
seed with a normal-count plant? Or does the plant have to reproduce
vegetatively for a while until there is another receptive brother or
sister with whom to mate?
6. How much messing around with chromosome numbers does it take before the
morphological differences are large enough to produce a new genus?

Please take pity on me. When I went to school all this was very new. Come
to think of it Darwin was new stuff back in those days.

Ted.

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From: lbmkjm at yahoo.com (brian lee) on 2008.01.08 at 01:48:24(16932)
Dear Ted,

Aloha. I think the best thing for you to do is to
look at Botany Online...it will help you on some of
the questions you pose.

In a nutshell, aneuploidy messes things up. In
humans, tumors and Down's Syndrome are examples. In
plants, death or deviant growth patterns are observed.

Aloha,

Leland

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From: Thomas.Croat at mobot.org (Tom Croat) on 2008.01.09 at 12:35:37(16937)
Dear Ted:

In our breeding studies here at the Missouri Botanical Gardens
we have found that intersectional crosses are rare, usually impossible
so the chromosome counts are not the only determining factor because
several sections share 2n0. Also aneuploidy appears to be in evidence
in sect. Porphyrochitonium which has chromosome levels of 28,29,30, 31
for example and these numbers can arrive by unequal crossing and through
the production of triploids which can cross because they have a full
complement of chromosomes. Really we ought to get Dick Sheffer to
expound on this. That is his area of expertice.

Tom

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From: agrsuw at ku.ac.th (agrsuw at ku.ac.th) on 2008.01.10 at 01:49:37(16939)
Dear Ted,

I really like your questions. I would like to answer your questions as
followed:

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From: ted.held at us.henkel.com (ted.held at us.henkel.com) on 2008.01.10 at 10:26:37(16942)
Dear Surawit,

Thank you for your reply. It looks like there is much information"out
there" about this science that has been hidden from me all these years. I
think I'll try Leland's advice as well, and think about what you have
written.

My response is humble and I have a number of new questions now that will
only add to my perplexity. Here are a few.

1. How reliable are chromosome counts, statistically? How many cells do
you need to count before you are satisfied that you have the right number?
2. Is it possible to have a nuisance cell or two that show a different
count from others from the same plant? I mean, what do you do if you
count, say 20 cells with 2n = 40 and one with 2n = 42?
3. How easy is it to break a chromosome in the process of performing the
preparation and root tip crush?

I'd better stop now.

Ted.

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From: agrsuw at ku.ac.th (agrsuw at ku.ac.th) on 2008.01.10 at 23:23:43(16944)
Dear Ted,

The following is my answer to your questions.
]
Quoting ted.held at us.henkel.com:

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From: pjm at gol.com (Peter Matthews) on 2008.01.13 at 19:19:41(16950)
Dear Ted,

>1. How reliable are chromosome counts, statistically? How many cells do
>you need to count before you are satisfied that you have the right number?

Some kinds of plants are more stable than others, but many plants (like
Colocasia eesculenta - taro) are very stable - i.e. one clear count on
one cell from one tip is likely to be the full story. Ferns with
hundreds of tiny similar-looking chromosomes are hard to count
accurately, and may also be more unstable in terms of number.

>2. Is it possible to have a nuisance cell or two that show a different
>count from others from the same plant? I mean, what do you do if you
>count, say 20 cells with 2n = 40 and one with 2n = 42?

Count more cells, confirm, and report!

In my experience, this sort of thing is a reflection of poor preparations
with spilled chromosomes and difficult, inaccurate counting.

If the counts are all clear and accurate, and the unusual number is real,
then there could be some interest in counting many more cells to
establish a frequency of occurrence, and measure the instability in cell
divisions.

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