def GetChromOrder(sample_blocks):
    """
    Get a list of chroms in sorted order
    Parameters
    ----------
    sample_blocks : list of [hap_blocks]
       each hap_block is a dictionary with keys
       'pop', 'chrom', 'start', 'end'

    Returns
    -------
    chroms : list of int
       list of chromsomes in sorted order
    """
    chroms = set()
    for i in range(len(sample_blocks)):
        for sb in sample_blocks[i]:
            chroms.add(sb['chrom'])
    chroms = list(chroms)
    chroms.sort()
    return chroms