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HYB: Tetraploid Conversion

From: Sharon McAllister <73372.1745@compuserve.com>

Linda Mann wrote:

>  What would be the relative contribution of a doubled diploid pollen
>  source (reichenbachii) to the tetraploid SHINING WATERS?  I don't know
>  how to ask what I mean...Sharon, Jeff, others, how does the diploid
>  tetraploid cross probably match up the chromosomes? 

"Doubling" is better described as an unreduced gamete.  In this case, it
carried two full sets of I. reichenbachii chromosomes instead of just one. 

PROGENITOR itself would be likely to function as an amphidiploidlike
hybrid.  It is not, of course, a true amphidiploid.   The two sets of I.
reichenbachii chromosomes that PROGENITOR carries are most likely to pair
with each other, so that every offspring would get one complete set. 

So let's take a look back at SHINING WATERS, an advanced-generation hybrid.
  If you trace its pedigree back to species, it's 5/8 tetraploid species,
2/8 diploid species, and 1/8 unknown.  Some of its ancestors are true
amphidiploids but the highly homologous nature of the chromosomes of these
species suggests that the intervening generations of crosses have resulted
in mixed sets rather than pure ones.  Overall, it probably has more
"southern" chromosomes than "northern " ones.

With the two sets of I. reichenbachii chromosomes, PROGENITOR is
predominantly "northern".  Remember, though, that there are NO absolutes in
this type of work.  Some of the individual chromosome pairs of different
species are actually homologous and it is quite possible that some of
PROGENITOR's offspring have more or less than one full set of I.
reichenbachii chromosomes.   As the amoena trait for which PROGENITOR has
become so famous is dominant, perhaps we should be more concerning with the
overall percentage of "northern" chromosomes instead of just the ones
traceable to a single northern species.

>   Would this be a
>  case in which the reichenbachii chromosomes could/would/might stay
>  paired with each other?  (did I get that right?) & thus maybe show up as
>  a pair of X trait, where X is fitness here, with only half a maternal
>  weakness?  Help?? Somebody who can see what I am trying to get at,
>  please translate into some kind of English.

IF I understand the question <G> the answer is 'no'.  Homologous
chromosomes pair on meiosis, then separate so that one goes to each
resultant gamete.  

Few easy answers in the realm of maternal inheritance....

Sharon McAllister

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