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.Â
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.Â
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.Â
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.
Â
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.
Â
Thank you!
Â
El
--
Jamie V.
_______________________
KÃln (Cologne)
Germany
Zone 8
