def get_bowtie2_orientation(paired_end, strand):
    """ Determine bowtie2 orientation option given library's paired-end status and strandedness.
        Return a dict whose keys contain bowtie2 args """
    result = {}
    if paired_end:
        result['fr'] = None

    if strand == '+':
        result['norc'] = None
    elif strand == '-':
        result['nofw'] = None
    return result