@staticmethod
def highestFrequenciesMultiple(a, b):
    """
        How much does the most frequent nucleotide occur more than the second
        most?

        @param a: An C{OffsetBases} instance.
        @param b: An C{OffsetBases} instance.
        @return: A C{float} made from the divsion of the count of the most
            frequent nucleotide with the count of the second most in the
            combined counts. If there is only one nucleotide, return C{None}.
        """
    counts = a._counts + b._counts
    if len(counts) == 1:
        return None
    else:
        orderedCounts = counts.most_common()
        return orderedCounts[0][1] / orderedCounts[1][1]
