Hi,

Thanks for the info, that's news to me, and I guess I'll have to do some
reading. I knew that 3N was bad for breeding because if you cross a 3N
with a 2N/4N, you get an aneuploid. But I still thought that most of
the time, the gametes would be okay. During meiosis one, there is
chromosome doubling and one reduction, and then another reduction in
meiosis II, what is it about 3N that makes the second reduction
difficult? If a nucleus had just one chromosome, during metaphase 1, it
would pair up with it's copy and separate, and then in metaphse 2, there
is no pairing required, but merely separation of the tetrad....right?

Cheers,
Xi

Rob Halgren wrote:
Xi Wang wrote:

Ploidy refers to how many sets of chromosomes a cell nucleus contains.
Usually, every cell has two copies of a chromosome, and is designated
2N. Usually, higher ploidy number means more robust plant (sequoiae
are 6N and are huge trees, and some of the most robust)- if some genes
get damaged, they have more backup genes to work with. However, a 3N
plant can only produce progeny with a 3N plant, and 4N plants,
preferably with other 4N plants.


3N plants (triploids) are notoriously infertile. Regardless of what you
cross them with. Even ploidy (2,4... etc) are more fertile because they
can properly pair off chromosomes during meiosis.

Rob