Meiotic Chromosome Preparation

The study of chromosomes at meiosis in humans commenced in 1956, when Ford and Hamerton (1) published the first pictures of metaphase I complements of human spermatocytes prepared by “squashing,”the only technique available to the meiotic cytogeneticist at that time. A major advance in technique took place, however, when“air-drying”of fixed spermatocytes in suspension superseded squashing (2 ), and this remains the preferred method for preparing human chromosomes for analysis at metaphase I (MI) and metaphase II (MII). The method gives enhanced spreading of the meiotic bivalents at MI, enabling chiasmata to be analyzed and counted, and with the application of C- or Q-banding methods, identification of specific bivalents is made possible. This is also a stage at which structural rearrangements or numerical anomalies can be identified by the univalent, trivalent, quadrivalent, or other multivalent configurations produced. Again, this process of identification being greatly aided by the application of C- or Q- banding techniques. In more recent times, studies have been carried out in which in situ hybridization of specific probes to MI bivalents has been used (3 ) and in situ nick translation procedures have been applied, for studies of the XY bivalent in particular (4 ).