def skew(gene_sequence, end_index):
    """ Calculate the difference between the quantity of G bases and the quantity of C bases. Helps to determine the effect of deamination and where 'ori' might lie.

    Args:
    gene_sequence: string. The DNA string on which to calculate the skew. Will most likely be the entire genome.
    end_index: int. The stopping point for calculating the skew.

    Returns: 
    skew: int. The difference between G and C bases in this gene_sequence.
    """
    return gene_sequence[0:end_index].count('G') - gene_sequence[0:end_index
        ].count('C')
