A replicative and synthetic chromosomal unit-the modern concept of the chromomere

present-day discussions on chromosomal structure and function the old term chromomere’ (Fol 1891) is seldom mentioned and it may be debated whether at is still desirable to use such a term. Conventionally it describes the bead-like concentrations of chromatin linearly arranged along the chromosomal thread, without implications as to the structural basis of such a discontinuity. Two alternative interpretations of the chromomeric organization of the chromosome have been suggested, one in which the chromomeres were regarded as definite chromosomal bodies, different from the interchromomeric regions of the chromosome, and one which considered the chromomeres as structures resulting only from the local coiling of a continuous chromosomal thread. Neither the chromomere hypothesis (Belling 1928; Bridges 1935; Pontecorvo 1944) nor the chromonema hypothesis (Ris 1945) has been finally and universally accepted. This is because the morphological and cytogenetical evidence previously available was insufficient to extend our knowledge of chromosomal structure down to the molecular level. New approaches in this direction have recently been made by the combined use of cytological, autoradiographic and photometric methods. They draw new attention to the chromomere.