def mutate(self, chromosomes, p_mutate):
assert <NUM_LIT:0> <= p_mutate <= <NUM_LIT:1><EOL>for chromosome in chromosomes:<EOL><INDENT>chromosome.mutate(p_mutate)<EOL><DEDENT>
Call every chromosome's ``mutate`` method. 

p_mutate:  probability of mutation in [0, 1]