def is_chr_prefixed(bam_data):
    """Check if chromosome names are prefixed with "chr"

    Args:
        bam_data (pysam.AlignmeentFile obj)
    Returns:
        is_prefixed (bool): True if prefixed.
    """
    header_dict = bam_data.header
    chromosome_names = header_dict["SQ"]

    is_prefixed = False
    if chromosome_names[0]["SN"].startswith("chr"):
        is_prefixed = True

    return is_prefixed