Viewing post #1737226 by admmad

clockworkhawkins said:
have you heard the terms triploid block and triploid bridge? I've read that its been suggested that the triploid is the next stage in evolution. that its essentially waiting for the correct gamete formations. at first i thought it was plausible but now I disagree.

I assume a nonreducing gamete flower needs to be met with other 2n gametes to preform the switch to tetraploid. however if the triploids are spawned from 2n x 1n = 33 pair then they would also be carrying atleast the genetic probability for 2n given to it by 1 of its parents.

my next assumption delves into the realm of science fiction. given a perfect series of line breeding where a large gamete formation was not just plausible but the norm rather than the rarity could we assume that perhaps a dodecaploid giving off 12n could actually hybridize higher up its classification. a theoretical example being.

two plants being 12n gamete in the family Asphodelaceae. obviously you have genetic misconfiguration but given a larger gene pool would there not be a higher likely-hood of success?

Triploid block is often mentioned as being present in daylilies. It is not present. When a triploid block is present in a plant species crosses between diploid and tetraploids do not produce triploids but rarely produce tetraploids. So in a species with a triploid block all (or more reasonably nearly all) seedlings produced from crosses of diploids with tetraploids would be tetraploids. In daylilies Arisumi showed that crosses between diploid and tetraploid daylilies rarely produce seedlings but when they do they are triploids not tetraploids.

Triploid bridges are considered as one way for natural tetraploids to be produced. The standard scientific consensus was that triploids were sterile. However, although triploids are more or less sterile they are not necessarily 100.0% sterile all the time or in all species. Therefore it is now considered that natural triploids may be one possible mechanism to produce natural tetraploids.

Tetraploids do not typically have normal fertility. Newly created higher polyploids presumably would have even lower fertility. Arisumi created one hexaploid . It was completely sterile in crosses with diploids, triploids and tetraploids and could not be crossed with itself.