The breakpoint of TB-8Lc was determined by examining the pachytene stage of an L289 x TB-8Lc hybrid. Materials were kindly supplied by B.-Y. Lin. A modification of the smear technique (C. R. Burnham, Maize for Biol. Res., p.107, 1982) was used. Good pachytene figures were photographed and enlarged. The length of the short arm and the length from centromere to the breakpoint of the long arm were traced. The unpaired long arm region was not measurable, so the physical length of the long arm could not be directly determined. Since the arm ratio is 1 to 3.2 for the short and long arms of chromosome eight, respectively (M. M. Rhoades, J. Hered. 41:58-67, 1950), the physical length of the long arm can be calculated by measuring the short arm. Distance between the centromere and the breakpoint, taken from ten measurable figures, was divided by the calculated length of the long arm, giving a breakpoint position on the long arm at 0.24 ± 0.05.
Ming T. Chang and J. B. Beckett
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