Fig. 4. IdU incorporation dynamics in the telomere of Tel/+ polytene chromosome X. (Top) Hoechst staining of DNA; (Middle) IdU incorporation pattern; (Bottom) merged image. IdU incorporation at the discontinuous labeling phase: (A-C) all over the telomere; (D-F) the cap region still replicates; (G-I) telomeric regions no longer incorporate the label by the beginning of the late S phase; (J-L) replication of the chromosome tip is completed prior to the replication termination in the IH regions. Dashed lines, TAS repeats; solid lines, marker regions.