Subject: What causes the special alignment of chromosomes during metaphase I ?

Chromosome alignment during metaphase I is sharply different from that of 
metaphase II or of mitotic metaphase. Do the chiasmata have something to do 
with this? If so, why don't they do the same thing during metaphase II? I'm 
wondering if the evolution of both crossing-over and the special alignment in 
metaphase I -- the main mechanical differences between meiosis and mitosis -- 
happened at the same time, via the same agent. Just curious.

Re: What causes the special alignment of chromosomes during metaphase I ?