Efficiency of chromosome bi-orientation during unperturbed M I revealed by KT tracking.
(A-D) All KTs of a representative spermatocyte expressing Mis12-EGFP and His2Av-mRFP were tracked during M I and assigned to chromosomes. (A) The KT tracks observed during the indicated phases are displayed as an overlay on the still frames from the end of the corresponding phases. Tracks are displayed with a color code reflecting VKT from slow (blue) to fast (red). (B) VKT plotted over time. (C) AKT plotted over time. (D) DKT plotted over time. Black dotted lines indicate division phase transitions. (E) Average DKT at late metaphase I (+/- s.d., n = 6 cells). DKT in case of the small chromosome 4 is less than in other bivalents (XY, chr 2 and chr 3). (F, G) Two distinct events of re-orientation of a KT pair during M I are illustrated with still frames oriented so that the spindle axis is horizontal. The KT tracks over the preceding two time points are superimposed on the images. Yellow arrows indicate the direction of movement of the re-orienting KT, which is to the right in the top panel and to the left after re-orientation in the bottom panel. The time interval separating the two still frames is indicated (minutes:seconds) Scale bars = 2 μm.