def count_mismatches_after_variant(reference_suffix, cdna_suffix):
    """
    Computes the number of mismatching nucleotides between two cDNA sequences after a variant locus.

    Parameters
    ----------
    reference_suffix : str
        cDNA sequence of a reference transcript after a variant locus

    cdna_suffix : str
        cDNA sequence detected from RNAseq after a variant locus
    """

    len_diff = len(cdna_suffix) - len(reference_suffix)

    # if the reference is shorter than the read, the read runs into the intron - these count as
    # mismatches
    return sum(xi != yi for (xi, yi) in zip(reference_suffix, cdna_suffix)) + max(0, len_diff)