Edited by Jasper Rine, University of California, Berkeley, CA, and approved March 5, 2021 (received for review November 5, 2020)How repressive heterochromatic states propagate along chromosomes and are subsequently maintained for many cell divisions remain important unanswered questions in biology. Combining mathematical modeling and single-cell measurements, we find that heterochromatin does not propagate in a purely linear manner as often assumed. Rather, sudden transitions can affect large domains globally at once. We suggest this is due to long-range interactions that bring distant...…Edited by Jasper Rine, University of California, Berkeley, CA, and approved March 5, 2021 (received for review November 5, 2020)How repressive heterochromatic states propagate along chromosomes and are subsequently maintained for many cell divisions remain important unanswered questions in biology. Combining mathematical modeling and single-cell measurements, we find that heterochromatin does not propagate in a purely linear manner as often assumed. Rather, sudden transitions can affect large domains globally at once. We suggest this is due to long-range interactions that bring distant...WW…