Correction to my last post: " the problem is that triploids DO NOT produce haploid gametes" On Wed, Jan 14, 2015 at 7:10 AM, Nicholas plummer <nickplummer@gmail.com> wrote: > 2n means that each chromosome is present in two copies (i.e. diploid). > The chromosome count of a triploid should be indicated as 3n=33. Saying > that a triploid has a chromosome count of 2n=33 is a contradiction in > terms. > > A haploid gamete would be n=11, indicating a single copy of each > chromosome, and the problem is that triploids produce haploid gametes. > They produce gametes with an unstable chromosome count, some chromosomes in > a single copy, and some in more than one. Among polyploids, plants with > even ploidy (2N, 4N, etc) tend to be fertile, while those with odd ploidy > (3n, 5n, etc) tend to be sterile. > > Various websites suggest that H. petiolatum has a chromosome count of 55, > making it a pentaploid, 5n = 55. If there are 77 chromosomes, it would be > septaploid, 7n=77. In any event, I'm pretty sure that its chromosome count > should not be presented as "2n=[some number]", because implies two copies > of each chromosome, when H petiolatum will actually have 5 (or more) > copies. > > What I find confusing about Hippeastrum breeding is the repeated claim on > various websites that diploid species cannot be successfully crossed with > the big commercial hybrids, because the commercial hybrids are tetraploid. > I would have expected the offspring of such a cross to be viable, though > sterile, triploids. If those crosses do not produced offspring, it > suggests that there is something else going on. > > Nick > > On Tue, Jan 13, 2015 at 10:30 AM, James SHIELDS <jshields46074@gmail.com> > wrote: > >> "2n" just means just the whole set of chromosomes in the plant's cells. >> For a diploid of 2n=22 species, the triploids have a total of 33 >> chromosomes per cell, so 2n=33 for those triploid sorts. It also suggests >> why most triploids and why petiolatum with 2n=77 do not often set seeds. >> >> Jim S. >> >