ABSTRACT
The fertility of a hybrid may also be reduced by irregularities in meiosis of germ line cells. Conventional light microscopy may reveal that chromosomes pair regularly during meiotic prophase, but fail to form chiasmata due to problems of homology arising from structural or numerical rearrangements of the genome, or to impairment of the mechanism of chiasma formation due to genic imbalance resulting from hybridity. Recently, detailed observations have been made on pachytene pairing in this hybrid using the relatively new technique of whole-mount surface spreading of synaptonemal complexes (SC). The inability to detect pachytene loops in the three largest bivalents prompted the use of a higher resolution technique, namely, three-dimensional reconstruction of SCs from serial electron micrographs. An account of chromosome pairing and fertility in hybrids would not be complete without mention of some of the pioneering work on the biochemistry of meiosis and, more specifically, on the biochemistry of chromosome pairing itself.
