Re: chromosome count vs ploidy



Dennis Kramb <dkramb@badbear.com> wrote:
  Several of them (such as I. aphylla, I.
croatica, I. cypriana) are listed as 2n=48.  Am I wrong in thinking this
should be 4n=48 ?  Whenever I've seen tetraploid chromosome counts written
it's always been with the 4n nomenclature.

 

Scientific litterature has a long tradition of using 2n as whatever is normal for the species.  I will agree that this does not make sense, and and sometimes tradition should give way.

A slightly better way that is commonly used is

2n=4x=whatever number is common in the species.

I used to work with Tripsicum dactyloides, eastern gama grass.  In that species, there are wild diploids, triploids, and tetraploids in the wild, all in roughly equal numbers.  the triploids, and many tetraploids, are apomictic (set seeds assexually) so you can't go by fertility.  You must count chromosomes for each plant.  In that species, the idea of 2n being the norm for the species is ridiculous.  There is no norm.

Walter


Do you Yahoo!?
Yahoo! Mail is new and improved - Check it out!
Yahoo! Groups Sponsor
ADVERTISEMENT
click here

Yahoo! Groups Links
Other Mailing lists | Author Index | Date Index | Subject Index | Thread Index