Date: Mon, 23 Feb 1998 15:05:13 -0700 From: ricell@juno.com To: cp@opus.hpl.hp.com Message-Id: <aabcdefg726$foo@default> Subject: Re: On Cultivars (and Taxa)
Jan,
>> However, once
>> one starts to cross plants that are themselves hybrids, there
>> should in theory be significant variation in the offspring.
>
>Why? A breeder does not cross populations with populations but
>individuals with individuals. The variation in each hybrid generation
>is always between the two parents that constitute the extreme poles
>of the range.
First, I am assuming that the intraspecies genetic variation is
significantly less than the interspecies genetic variation.
Using the example I cited of (S. x mitchelliana) x (S. x formosa),
for any given gene, S. x mitchelliana will have a S. purpurea allele
and a S. leucophylla allele which I will designate as LP (I'm
assuming this is an F1 cross) while S. x formosa will have a S.
minor allele and a S. psittacina allele which I'll designate as MPs.
Now, if we cross these two plants we have 4 possible
combinations LM, LPs, PM, PPs. If this gene affects something
like say pitcher height then the variation between LM and PPs
could be dramatic.
I think this is analagous to why F1 hybrids are quite consistent
in appearance while F2 hybrids will have much greater variation.
>> Is this
>> one of those cases where there is a lot of "theoretical variation"
>> but in practice all (for example) (S. x mitchelliana) x (S. x
>formosa)
>> crosses look pretty much the same?
>
>You do not talk about cultivars in this case. Both hybrids are taxa,
>and at least theoretically, the complex hybrid is again a taxon. This
>latter taxon will include all intermediates between the species
>involved (_S.leucophylla, minor, psittacina, purpurea_).
True, I am not talking about cultivars in this case (or above). And
I think I am questioning the usfullness of giving a name to a group
of plants that includes all intermediates between those 4 species.
If my understanding of cultivar is correct, there should
be no genetic variation of cultivars (or the only genetic variation
should be from spontaneous mutation of the cells that allow asexual
reproduction?)
>
>> On a related note. Are many of the morphologic characters of
>> Nepenthes sex linked? If they are, then it seems that having
>> different names for essentially the same cross (only by opposite
>> sexed parents) makes sense.
>
>Not at all if they are treated as taxa. In this case, the direction
>(and any repetitions) of the cross is entirely immaterial.
Perhaps this example will elucidate my confusion: Are
N. x wrigleyana and N. x coccinea examples of taxa or cultivars
or neither? I was thinking these were considered taxa and the
only difference between them was the sex of the parents.
Richard Ellis "ricell@juno.com"
Boulder, CO
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