[southtown]

这是一段DNA序列转换成数字的程序，望高手指教第二行程序是什么意思？:lovely:

A='aggcacggaaaaacgggaataacggaggaggacttggcacggcattacacggaggacgaggtaaaggaggcttgtctacggccggaagtgaagggggatatgaccgcttgg';

A=(A=='a')+(A=='t')*2+(A=='c')*3+(A=='g')*4;