A hypothesis for the origin and evolution of chromomere DNA

A hypothesis for explaining the possible origin and evolution of chromomeric DNA is proposed. The hypothesis postulates that, originally, the chromomeric DNA has consisted of one transcriptive and replicative unit. The replication of chromomeric DNA is terminated at the regulatory segments of the transcriptional unit, which thus form the border line between the interchromomere and chromomere. The amount of DNA of most chromomeres is proposed to be increased by repeated tandem duplications of the chromomere loop. The connection with initiation and regulatory segments outside the chromomere makes the first transcriptional unit of the loop the most essential gene. The structure of the first unit is controlled by selection, while the other repeated units of the loop DNA are randomly differentiated. Exact redundancy of units is reduced but shorter segments still remain identical enough for the formation of rings. Besides the first active unit the chromomeric loop may include also other potential genes, which can be activated by chromosomal rearrangements.