Schematic illustration of dual-phase clonal expansion of cells that lose first one (yellow) then the second (orange) supernumerary 3p21 copy in #3/KH39 MCH propagated in vitro during 0, 3 and 9 weeks (0w, 3w and 9w, respectively). Chr3 constitution and derivation of each clone is shown at the top. 3p21 is indicated as a black band on 3p. In comparison to KH39, which has 2 copies of this region, 4, 3 and 2 copies in a clone correspond to 2, 1 and no supernumerary copies, respectively. The cells representing such clones are shown below in green, yellow and orange colors, respectively. Clone c5, derived from c2 by a chr3 rearrangement (M4), gave rise to c6 by loss of M1. Loss of one normal chr3 in c2 led to expansion of c4. Translocation of the long arm of chromosome 1 (white on M3) to 3q in c3 produced clone c7, which expanded as the largest clone.