Fig. 2. Duration of prometaphase I under conditions that may trigger a spindle checkpoint. (A) Duration of prometaphase I was estimated as the interval spanning between the beginning of chromosome condensation and the onset of anaphase I. Four different conditions including wild-type untreated cells, wild-type cells treated with colchicine, and cells containing two [C(3L);C(3R)] or four [C(2L);C(2R);C(3L);C(3R)] univalent chromosomes were studied. Each line shows the number of cells followed in each single culture, together with the average (x), standard deviation (s.d.) and range of prometaphase length. The cumulative average of all the cultures from the same experiment and the corresponding standard deviation are also shown (X ± S.D.). Colchicine treatment of wild-type spermatocytes, as well as the presence of four univalents result in a delay of around 16 min, with respect to the control, while the presence of two univalents has no effect. (B) Graphic representation of the data presented in (A) showing the frequency distribution of the duration of prometaphase in the four experimental conditions studied.