The <i>XY</i> bivalent in human male meiosis

Abstract

Summary The X Y bivalent could eady be recognized in diakinesis and first metaphase in air‐dried preparations. The X and Y were clearly separated in varying proportions of these cells but probably more often in cells in the later stages. No chiasma could be demonstrated with certainty between X and Y . The Y chromosome had in some cells a clear constriction at its distal end which might indicate the centromere, and it was often bent in a characteristic way. The X chromosome was also typically bent in some cells, and sometimes demonstrated one less contracted part close to the Y and one contracted and irregularly curved distal part. It is tentatively suggested that the long arm of Y is associated with the short arm of X . The point is stressed that the problem of the existence of homologous sections of the X and Y chromosomes in man cannot be solved by present cytological observations in the absence of genetical evidence.