El,
in the case of the versicolor x laevigata hybrids, you are generally
getting sterile off-spring on the diploid level. The reason they tend to
be sterile, and I say tend, as there are rare exceptions of partial fertility,
is the imbalance in the chromosomes. When gametes form, the dividing cells
have to have an analogous pairing of the chromosomes in order to successfully
divide. This is to say that the chromosomes need a partner, which balances
them out during meiosis.
What we often forget is, chromosomes are far
from identical, but come rather in pairs which are matched (analagous) to each
other. This allows them to react with each other (exchange genetic
material) and go their seperate ways during cell division (meitosis and
meiosos). Without this, the cell cannot properly divide and genetic
variation would not be possible.
In the case of a diploid versilaev you
have 54 chromosomes from versicolor, but only 16 chromosomes from
laevigata. Even if the 16 chromosomes found balancing partners from the
other parent (which rarely happens), we still have many more versicolor
chromosomes without partners. Thus, they are sterile. Incomplete
meiosis. These plants are capable of living, just incapable of producing
viable gametes.
The way around this is to double the chromosomes to the
tetraploid level, then you will have not only enough chromosomes to go around,
but the right partners.
Go to Tomas Tambergs website to get a little bit
of general info on these crosses.
http://www.tamberg.homepage.t-online.de/
There
is an English language section.
Hope this
helps,
Jamie
Am 01.01.2011 21:17, schrieb Eleanor Hutchison:
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
--
Jamie V.
_______________________
KÃln (Cologne)
Germany
Zone 8
