Re:Auto-tetraploid versus amphidiploid was Hyb spots
iris@hort.net
  • Subject: Re:Auto-tetraploid versus amphidiploid was Hyb spots
  • From: C* C* <i*@aim.com>
  • Date: Thu, 28 Feb 2013 11:46:52 -0500 (EST)
We had been discussing  aphylla  X TB hybrids and fertility.
Actually, it turns out that full tetraploids, (autotetraploids) with four identical genes, have much reduced fertility compared to amphidiploids, or straight diploids.
This is because during meiosis (forming of gametes, eggs and pollen) four sets of identical genes often form tetravalents. And during first stage of meiosis, either all of these four genes go into one cell, or the other, leaving no copies in the other cell. When there is small differences in the four sets of genes, of a particular chromosome, you get two bivalents and so proper division during meiosis
Now remember, most tetraploid iris, at least the TB iris , have multiple species involved in their creation, so probably a number of genes from different species, with enough of a difference, and enough of a similarity, to pair up as fertile bivalents , rather then tetravalents during meiosis.
Also almost all ( I'd say all, but there probably an exception or several out there somewhere) fertile tetraploids found in nature, are a result of an inter species hybrids, and thus are amphidiploids, rather then autotetraploids.
So fertile 4x 48 iris are should basically be considered amphidiploids. The infertile ones are probably autotetraploids. 

Look up "fertility in autotetraploids"

Chuck Chapman

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