Hi
I had this question elswhere but it might be better to have it here.
Often one talk about that there is a dubble set of cromosons one from mother, n, and one from father, n, totaly having 2n.
Plant can be treated so that they get 4n.
Is there spieces with 4n in the Slipper family? Not hybrids or treated spieces, but "naturally accuring"? Or is the cromosone count very different between the different spieces?
If so how common is it?

Has it been seen in Cyps aswell? Could that be part of incompatible problems between spiecies within the Cyp family?


Joakim

I don't kow how common it is but it does occur in nature, not only with slippers but other living things as well.

Hello, I just read an article on this very subject, here's what I learned:

-polyploids do occur in nature, although they are relatively uncommon
-triploids are the most common of the natural polyploids. They usually result from an unreduced gamete(2n) merging with a regular gamete(n) to form a triploid offspring(3n). These triploids are usually sterile or near-sterile due to the aneuploid gametes they produce (gametes having an irregular chromosome number).
-tetraploids are known to occur in nature but they are extremely rare. This is because they originate from either i) the merging of two unreduced gametes(2n) to form a tetraploid (4n), or ii) the spontaneous doubling of chromosomes after embryotic formation(this is what happens when colchicine is used to artificially induce polyploidy).

Unreduced gametes are extremely rare, although I don't know if their frequency in nature has been determined. The article I read (Mehlquist, 1974, On Polyploidy in Orchids... IN Orchids, Scientific Studies Ed. Withner.) provided an example based on unreduced gametes occuring 1 in every 1000 times. If this is the case, then assuming all the unreduced gametes produce viable embryos (this is a big assumption and probably not the case), the odds of a tetraploid resulting from any two random gametes is 1 in 1,000,000. Triploids are much more likely, occuring 1 in every 1000 times (because they only require one unreduced gamete). And, even when a tetraploid is created, its slow growth is a detriment to its survival, as it can be easily crowded out by its diploid siblings.

As for cypripediums, all share a common diploid chromosome number of 2n=20. However, the total size of the genome can vary considerably (Cox et al. 1998). Cypripedium is by far the most widespread of the slipper genera and one can infer that this has led to more distinct speciation than the other genera that inhabit relatively small ranges. This may contribute to the increased difficulty in breeding Cypripedium hybrids.

--Stephen

Thanks for the nice information Stephen

It then seems as if treatment with colchicine would not be an advantage to get better agreement between different Cyps or did I miss anything?

Kind regards
Joakim

[b]Crossing barriers, or at least hybrid vigor barriers between Cyp species might be due to greater genetic divergence between the species more than anything else. The chromosome number appears to be constant; nonetheless, artificial generation of allopolyploids (polyploids arising from hybrid origins) might work well for wide crosses, such as between margaritaceum and calceolus -- this is because allopolyploids get a set of chromosomes from each parent, creating a condition known as 'fixed heterozygosity', which often permits hybrid vigor. Hybrid vigor is also the phenomenon one sees when crossing, say, Paph bellatulum with Paph delenatii to get x Vanda M. Pearman, clearly a more vigorous growr than either parent. Hybrid vigor gets 'multiplied' and can lead to a diversity of plant forms, each with vigor. That's because different copies of the same genes in allopolyploids get silenced, often randomly, to balance cellular activities. Note still that Cyp genomes are really big, so doubling them will make them even bigger. The larger the genome size, in general with plants, the greater the generation time (=time between flowering and seed and back again). For example, pine trees have huge genomes, and obviously long generation times. Some oncidium-type orchids, on the other hand, are reproted to have relatively tiny genomes, and they can have really short generation times.

Best from Beskriver

Thanks a lot for the information I hope more than I enjoid it :) I found it very educational and informative.

Joakim

Concerning creating 4n Cyps to further hybridization efforts: this may help as the chromosome count is not the only barrier encountered in making hybrids. Having two complete sets of chromosomes may allow hybridization just as it has in Paphs, because each chromosome type has a homologue to pair with. As for generation time, while genome size does correlate somewhat with generation time it does not always work that way. For instance, tetraploid Phalaenopsis plants may mature under proper culture faster than many diploids. With selection for faster growth, tetraploid Paphs and Phrags may grow at about the same rate as diploids. Another good example: many anurans and lung fish have very large genomes but mature much faster and live shorter lives than many Eutherian mammals including humans. Also, Paphs and many Phrags have larger genomes than many Phals but grow and mature faster.
Dean Stock

Oops! Sorry, Conserning creating 4n allotetraploids, I said about the same thing that Besk did but not nearly as well!!!! Got to read the whole thing before I jump in. Blame it on old age and poor vision!!!
Dean Stock

:) :)
It is nice to hear the same thing told in a different way it always improve understanding.
Joakim