The compaction of chromatin that occurs when cells enter mitosis is probably the 
most iconic process of dividing cells. Mitotic chromosomal compaction or 
'condensation' is functionally linked to resolution of chromosomal intertwines, 
transcriptional shut-off and complete segregation of chromosomes. At present, 
understanding of the molecular events required to convert interphase chromatin 
into mitotic chromosomes is limited. Here, we review recent advances in the 
field, focusing on potential chromosomal compaction mechanisms and their 
importance to chromosome segregation. We propose a model of how metaphase 
chromosomes could be shaped based on the enzymatic activities of condensin and 
topoisomerase II in overwinding and relaxation of the DNA fiber during mitosis. 
We suggest that condensin overwinding is an important requirement for intertwine 
resolution by topoisomerase II and, together with the inhibition of 
transcription, contributes to cytological mitotic chromosome appearance or 
'condensation'.