Write a Python script that outputs all pairwise dissimilarity 
distances under the Jukes Cantor model. The input is a set of aligned
sequences in a file called "dna_fasta.txt". The formula for the
evolutionary distance under Jukes Cantor is 

dij = -3/4 ln(1 - (4/3)pij) 

where pij = (number of mismatches)/(number of matches + number of mismatches)

Submit a hardcopy on Mar 24th in class.

Your solution must work for any number of sequences.