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RE: ploidy

Please allow me to step in.  

Paul said:
> Ben  let me see if I understand you correctly.  Plants with 
> redundant genes 
> do not follow mendelian genetics? Is this so?
Polploid genetics still follow standard Mendelian rules.  There are only two
strands of DNA per chromosome.  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.

Using the upper case letter B to represent one allelic alternative, and the
lower case letter b as the other, in a diploid, you get three possibilities:
BB (homozygote)
Bb (heterozygote)
bb (homozygote)

In a tetraploid, you have five possibilities:
BBBB (homozygote, quadriplex)
BBBb (triplex heterozygote)
BBbb (duplex het)
Bbbb (simplex het)
bbbb (homozygote, nulliplex)

The probabilities get quite complicated when you combine these.  In
addition, with interspecific hybrids, chromosome pairing is frequently not
perfect, so the predicted Mendelian events don't always fall out at the
expected ratios.  

Finally, it's hard enough to make enough seed to enable a grow-out of a
large enough population of diploid seedlings to find that
"needle-in-the-haystack".  The numbers needed for polyploids are enormous.  

But it's all still Mendelian.  Two alternatives per gene locus.  

Rick Grazzini
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