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Re: Tetraploids exist !


>By the way 2: nearly all hostas are diploids

It's nice to know that nearly all hostas are diploids.  Could you 
pleas tell us which ones are not diploids?

Just because hostas look and behave like diploids doesn't mean they 
aren't amphidiploids, also refered to as allo-tetraploids.  With 60 
chromosomes hostas are almost certainly amphidiploids. 
Allo-tetraploids are called amphidiploids because they look like they 
are diploids when you look at their meiosis - you see typical bivalent 
pairing.  If you cross two species, lets say species A and species B, 
then the F1 hybrid has one set of A chromosomes and one set of B 
chromosomes.  If Chromosome set A is not homologous with chromosme set 
B, then they don't pair during meiosis and the plant is infertile.  
Some people say sterile, but that is not the most correct term.  Now, 
if you double up that plants chromosome numbers the plant will have 
two sets of A chromosomes that can pair with each other and have two 
sets of B chromosomes that can pair with each other.  When you look at 
the cells undergoing meiosis you see a cell with twice the number of 
chromosomes as the two species, but each chromosome is undergoing 
bivalent pairing, thus the hybrid is fully fertile and it looks like a 
diploid.  Polyploidization has been a significent factor in the 
evolution of plants.  Since you are a fruit fly and yeast geneticist, 
NOT a higher plant geneticist, you are probably unaware of the 
significence of polyploidization in plants and how it occures.  For a 
long time botanist thought that the different species produced a 
diploid F1 and then sometime later there was natural doubling to the 
tet level.  However, we now know that this polyploidization in plants 
has come about by unreduced gametes.  The union of an unreduced egg 
with an unreduced pollen sperm cell gives instant rise to a fertile 
amphidiploid.  You might be interested to know that Luther Burbank, 
the great American horticulturist of the late 19th century and early 
20th century was the first to have this occure under controlled 
conditions with his introduction of the Garden Huckleberry or Wonder 
Berry by crossing two poisonous Solanaceae plants.  He repeated the 
cross for 13 years without ever getting a pod to set and then one day 
he got one pod to set with one seed and the resulting hybrid was fully 
fertile and true breeding, and, interestingly, it was not poisonous 
even though both parents were poisonous.  This is what we call an 
amphidiploid.  He gave a presentation of this event to a horticulture 
meeting in the early 20's, but, unfortunately, he wasn't a scientist 
and he was mostly ridiculed.  Today we know better.

Now, last year I planted a LARGE amount of ventricosa Aureomarginata 
seed and got very few seedlings.  I saved about ten or so of the more 
interesting seedlings.  The question is, are these going to be 
triploids or tetraploids?  These seedlings were as vigorous as 
vigorous seedlings from other crosses, but there wasn't anything about 
them to suggest they were tetraploid.

Joe Halinar
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