Re: Re: HYB: spots (was another terminology question)
iris@hort.net
  • Subject: Re: Re: HYB: spots (was another terminology question)
  • From: C* C* <i*@aim.com>
  • Date: Tue, 26 Feb 2013 23:54:14 -0500 (EST)
f Producing a viable embryo can happen with mismatched chromosomes, in some circumstances,and in some occasions, just as Sharon said. But this doesn't involve mismatched chromosomes pairing. And they have to pair to provide crossing over. Chromosomes have banding patterns on them involving condensed and more relaxed packing of the chromatin. Look up some photos of chromosomes to see what I mean.
They all have centromere and have two arms. One above the centomere (p arm) and an arm below the centomere, the q arm. The p arm is usually shorter then the q arm. To pair, the pattern of condensed, and relaxed sections, the position of the centromere, and the length of the two arms have to match. They start matching from the ends and work towards the centromere. But they only do this if the banding regions exactly match. Like two bar codes, exactly ( sometimes with out being exactly alike but nearly exactly alike), at the two ends. If arms are slightly different in length, they will have a region bulging out, not attached anywhere. Thus when they do have crossing over, sections will be cut off and float around randomly in cells, unable to attach to anything, and randomly sort out. In the meantime, the loss of genes renders the cells unviable, and if used in a gamete, result in instant death. Well, not always. If organism survives, it is severely impaired. A number of diseases of this type ( from mispairing or chromosomes during meiosis) have been identified in humans. Look up "Cri du Chat syndrome" for one.
I can give you references for this if you like. I have a couple of genetic books here describing the whole process. 

So basically, no matching, no crossing over.

Chuck Chapman


-----Original Message-----
From: Linda Mann <lmann@lock-net.com>
To: iris <iris@hort.net>
Sent: Tue, Feb 26, 2013 5:49 pm
Subject: Re: [iris] Re: HYB: spots (was another terminology question)

From hortnet archives,  Fri, 28 Mar 1997
Crossing-over -- the physical exchange of segments of paired 
chromosomes.

 =
Usually homologous ones, but sometimes even mismatched ones yield a 
viable

embryo.

Sharon McAllister


More on the same day re: allo-, and autotetraploids, amphidiploids.
The general term TETRAPLOID simply means it has four sets of 
chromosomes.  It
tells us nothing about the types of chromosomes. It's the most 
appropriate term
for TBs, because after so many generations we just don't know which 
species

individual chromosome sets might have come from.


Linda M
Linda Mann

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