def getGC(basesCounter):
    """
    Description
    -----------
    Calculate GC percentage of the genome.

    Parameters
    ----------
    baseCounter : collections Counter object which has counts of each of the 
    nucleotide.

    Returns
    -------
    FLOAT, GC percentage value
    """
    totalBases = sum(basesCounter.values())
    try:
        GC = (float(basesCounter['G'] + basesCounter['C'])/(totalBases-basesCounter['N']))*100
    except KeyError:
        GC = (float(basesCounter['G'] + basesCounter['C'])/totalBases)*100
    return GC