HYB: Pentaploids
From: Sharon McAllister <73372.1745@compuserve.com>
Message text written by Bill Shear:
>I'm not sure how a pentaploid (5 sets of chromosomes) would be induced
chemically in a lab, especially in irises. The few known iris pentaploids
have resulted from unreduced triploid eggs fertilized by normal tetraploid
pollen, or vice-versa, or as unexplained accidents.
With 5 sets of chromosomes it would seem that three would have to come from
one parent and 2 from another. Or would it be possible for one set to come
from a normal diploid egg or pollen grain, and 4 from an unreduced
tetraploid gamete?
Sharon, some help here?<
Yes, the typical origin of a pentaploid is a cross of a triploid and
tetraploid in which the triploid gamete is unreduced. The "accidents" I've
investigated have involved tetraploid pod parents the presence of triploids
in the garden, so that the probable-but-unproven explanation is that the
pollen parent was triploid.
Some years ago, I was experimenting with Tom Wilkes' cochicine-induced
hexaploids. I believe that the seedlings I got by crossing them with
tetraploids were indeed pentaploid. Wilkes' purpose in producing
hexaploids was to use them with diploids to increase the tetraploid aril
gene pool. My thought was that the pentaploid route could be used in this
program much as the triploid route had been used in the development of the
tetraploid TBs. Unfortunately, time ran out on both of us.....
But to get back to the question of a normal diploid gamete combining with
an unreduced tetraploid gamete -- in the world of wide crosses, it seems
that almost anything is "possible". I suppose that the chances of getting
this combination would be comparable to that of getting the combination of
an unreduced diploid gamete and normal tetraploid gamete. In theory, the
fertility of the resultant pentaploid should be comparable to that of the
normal triploid so unless it had attention-getting features such a creation
might well pass undetected.
Sharon McAllister
73372.1745@compuserve.com
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