$VAR1 =  {
            'A' => [2,1,1],
            'T' => [1,3,1],
            'C' => [0,0,1],
            'G' => [1,0,1]
         };

So the size of the array is the same with the length of the string.

In my case I need the variation of it, namely the probability of the 
each base occur in the particular position:
$VAR =     {
            'A' => ['0.5','0.25','0.25'],
            'T' => ['0.25','0.75','0.25'],
            'C' => ['0','0','0.25'],
            'G' => ['0.25','0','0.25']
          }