Date: Wed, 18 Oct 2000 09:15:31 +1100 From: Miguel de Salas <mm_de@postoffice.utas.edu.au> To: cp@opus.hpl.hp.com Message-Id: <aabcdefg2999$foo@default> Subject: Re: _Drosera_ hybrids
<snip>
>is in many cases entirely wrong. *One* well documented case of a
>sterile hybrid (the widesperad _D. rotundifolia * anglica_, the
>parents of which have different ploidies resulting in aneuploid
>offspring) is balanced by eqally well documented, far more numerous
<snip>
Jan,
Unless I am misinformed, aneuploidy, as a form of polyploidy, refers only
to the presence of extra single chromosomes, as opposed to auto- and
allo-polyploidy, which refer to the multiplication of entire genomes.
Probably the best known case of aneuploidy is Down's syndrome.
The important thing to note here is that aneuploidy derives from a single
genome, i.e. most aneuploids are not only usually fertile, but normally
pass the condition on to their offspring.
When we cross D. rotundifolia (a diploid?) with D. intermedia (diploid
too?) we do get an infertile hybrid, as chromosomes in the diploid
offspring cannot find clear homologues to pair with. However, were we to
double the chromosome number, we would find a situation in which
chromosomes can pair up with the extra copies of themselves, producing
bivalents which separate correctly at meiosis.
When you state D. rotundifolia and D. anglica have different ploidies,
which is the polyploid? If we were to cross diploid with tetraploid, the
resulting offspring would be triploid, and triploids are generally
infertile (but rarely sterile).
However, I think aneuploid offspring don't arise normally just from
crossing parents with different ploidies, or different diploid chromosome
numbers.
Cheers!
Miguel de Salas
mailto:mm_de@postoffice.utas.edu.au
School of Plant Science,
University of Tasmania,
GPO Box 252-55, Hobart,
Tasmania, Australia, 7001.
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