Biology Question

Question

If a mutation merely doubled the number of chromosomes, the offspring would be born as a separate species from that of its parent. How are the two new species reproductively isolated?  Which type of reproductive isolation—prezygotic or postzygotic—would this be an example of? Which type of speciation—sympathic or allopatric—would this be an example of? Which two taxa are the two where recurrent entire genome duplication has occurred?

Answer 1

An offspring that is born completely (as opposed to chimerally) tetraploid, where the parents are diploid, can sometimes back breed with the diploid population. The resulting offspring, however, are triploid -- and triploids are sterile themselves, because they don't successfully segregate their chromosomes during meiosis. So the offspring would present a dead-end population, not a new species. This is seen in the domestic banana, for example: the black specks at the core of the fruit represent undeveloped seeds which would otherwise (in the diploid or tetraploid parents) fill the fruit skin with hard kernals, with little edible flesh between.

And there aren't "two new species" generated! Only the triploid is new.

The rest you can figure out from definitions, or look up?

One more thing you might miss: the highest known polyploid (plant) species is one of the mulberries, with 42n karyotype, if I recall. Weird how the Moraceae went to town on that process ...

-- Cheers, --Mr. d.