DNA序列翻译为蛋白质序列 perl script

#!/usr/bin/perl -w
my (%code)=(
    'GCC'=>'A',
        'GCA'=>'A',
        'GCT'=>'A',
        'GCG'=>'A',
    'CGT'=>'R',
        'CGC'=>'R',
        'CGA'=>'R',
        'CGG'=>'R',
        'AGA'=>'R',
        'AGG'=>'R',
    'AAT'=>'N',
        'AAC'=>'N',
    'GAT'=>'D',
        'GAC'=>'D',
    'TGT'=>'C',
        'TGC'=>'C',
    'GAA'=>'E',
        'GAG'=>'E',
    'GGT'=>'G',
        'GGC'=>'G',
        'GGA'=>'G',
        'GGG'=>'G',
    'CAT'=>'H',
        'CAC'=>'H',
    'ATT'=>'I',
        'ATC'=>'I',
        'ATA'=>'I',
    'TTA'=>'L',
        'TTG'=>'L',
        'CTT'=>'L',
        'CTC'=>'L',
        'CTA'=>'L',
        'CTG'=>'L',
    'AAA'=>'K',
        'AAG'=>'K',
    'ATG'=>'M',
    'TTT'=>'F',
        'TTC'=>'F',
    'CCT'=>'P',
        'CCC'=>'P',
        'CCA'=>'P',
        'CCG'=>'P',
    'TCT'=>'S',
        'TCC'=>'S',
        'TCA'=>'S',
        'TCG'=>'S',
        'AGT'=>'S',
        'AGC'=>'S',
    'ACT'=>'T',
        'ACC'=>'T',
        'ACA'=>'T',
        'ACG'=>'T',
    'TGG'=>'W',
    'TAT'=>'Y',
        'TAC'=>'Y',
    'TAA'=>'_',
        'TAG'=>'_',
        'TGA'=>'_',
        'GTT'=>'V',
        'GTC'=>'V',
        'GTA'=>'V',
        'GTG'=>'V',
        'CAA'=>'Q',
        'CAG'=>'Q',
    );
    open SEQ,"$ARGV[0]";
       while($seq=<SEQ>){
         $seq=s/\n//g;
         chomp($seq);
         my $protein = tra($seq);
         print"$protein\n";
       }
    close SEQ;

     sub tra {
         my($DNA)=@_ ;
         my $protein='';
        # my $p = length($DNA)/3 ;
        # my $m = sprintf ("%0.f",$p);
         for($i=0;$i<length($DNA)-2;$i+=3){
         $protein.=genecode(substr($DNA,$i,3));
         }
         return $protein;
     }

       sub genecode{
         my($nnn)=@_;
             $nnn=uc $nnn;#字符转化为大写
         if (exists $code{$nnn}){
            return $code{$nnn};
         }
         else{die"bad code '$nnn'!!\n";}
     }