2013考研英语二图表作文预测:出生率和婴儿死亡率

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　　Sometimes HMW DNA could not be efficiently digested by Hind III enzyme for the recovery of 100-300 kb DNA segments, which was probably caused by the following reasons: firstly, the histones in the chromosomes were not completely digested, the Hind III enzyme could access DNA to cut it, to solve this problem, we should prolong the digestion time to 15 min or add the concentration of proteinase K to 0.5 mg/ml; secondly, proteinase K was not completely inactivated by PMSF, thus proteinase K could inactivate Hind III enzyme, at this situation, the plugs should be washed time after time by TE solution containing PMSF; thirdly, the rudimental PMSF also could inactivate Hind III, so the plug should be adequately washed by TE solution without PMSF following the washing with TE solution containing PMSF.