Physical principles of chromosome segregation

The faithful separation of duplicated chromosomes into daughter cells is essential for life, yet how cells reliably accomplish this remains a deep physical puzzle. Chromosomes are long, densely packed polymers confined within a crowded cell, and their accurate partitioning depends both on the intrinsic physics of the polymer and on the action of motor-like protein complexes (SMCs) that actively reshape chromosome structure. Focusing on bacteria, I will present an energy-landscape framework that combines experimental contact-frequency maps with polymer physics to reconstruct the three-dimensional organization of chromosomes during replication. Our models reveal that the long-range compaction generated by SMC complexes drives distinct structural transitions that facilitate the segregation of duplicated chromosomes to opposite ends of the cylindrical bacterial cell. When SMC activity is removed, this transition fails, and the sister chromosomes instead align in parallel—a low-disorder state that physically resists separation and leaves a measurable fingerprint in contact maps. We argue that SMC activity widens the range of conditions under which chromosome segregation succeeds, buffering the process against the crowded and adhesive cellular environment. This work uncovers conserved physical principles underlying chromosome segregation and makes testable predictions for imaging and chromosome-contact experiments.