RE: ploidy
Rick:
>However, there are four sets of chromosomes in a tetraploid, rather
>than two, so that you have five possible combinations of alleles at
>each locus, rather than three.
Allow me to throw in some other considerations. I think Ben got
confused because he was thinking about segregation ratios from the
point of a autotetraploid rather then an ampidiploid. Segeration
ratios from autotetraploids can be variable. However, autotetraploids
are rarely fertile to any extent. With an amphidiploid every gene is
basically duplicated, like in an autotetraploid, but you get some
addition factors to consider with the five possible combinations you
mentioned.
In an amphidiploid the combination BBbb comes in two forms - BB//bb
and Bb//Bb, where the "//" seperates the two genomes. If you self the
Bb//Bb plant you can recover the recessive phenotype (15:1
dominant:recessive; 1/4 x 1/4), but if you self the BB//bb plant all
the progenies are dominant and of genotype BB//bb.
If you take a dominant complementary gene and throw in an inhibitor
gene and then duplicate that on the second genome, you can quickly see
how figuring out segregation ratios in an amphidiploid can become very
difficult. And a dominant complimentary gene with an inhibitor is a
SIMPLE system! Then, throw in some transposable elements to mess
things up and....
Joe Halinar
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