Hippeastrum ID query

Nicholas plummer nickplummer@gmail.com
Wed, 14 Jan 2015 04:11:46 PST
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.
>>
>



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