def chromosomes_from_fai(genome_fai):
    """
    Read a fasta index (fai) file and parse the input chromosomes.

    :param str genome_fai: Path to the fai file.
    :return: list of input chromosomes
    :rtype: list[str]
    """
    chromosomes = []
    with open(genome_fai) as fai_file:
        for line in fai_file:
            line = line.strip().split()
            chromosomes.append(line[0])
    return chromosomes