What is Aneuploidy?


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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