Prophase I continued.
<LI> In  Pachynema  (Pachy:  thick), the aligned homologous chromosomes
(bivalents)  continue  to  condense  and  'zipper'  together  in a
process  called  synapsis, forming tetrads which are held together
by   a  synaptonemal  complex.  Non-sister  chromatids  may  start
exchanging genetic material in a process called crossing over.
<LI> In  Diplonema  (Diplo:  double), the homologues begin to separate,
and chiasmata, regions where non-sister chromatids are intertwined
and crossing over occurs, become visible.
<LI> In  Diakinesis  (Dia:  across), the chiasmata terminalize (move to
the  end  of  the  tetrads).  The homologues separate further, and
centromeres   attach   the  chromosomes  to  spindle  fibers.  The
nucleolus and nuclear envelope break down.