def get_chromosome_priority(chrom, chrom_dict={}):
    """
    Return the chromosome priority
    
    Arguments:
        chrom (str): The cromosome name from the vcf
        chrom_dict (dict): A map of chromosome names and theis priority
    
    Return:
        priority (str): The priority for this chromosom
    """
    priority = '0'
    
    chrom = chrom.lstrip('chr')
    
    if chrom_dict:
        priority = chrom_dict.get(chrom, '0')
    
    else:
        try:
            if int(chrom) < 23:
                priority = chrom
        except ValueError:
            if chrom == 'X':
                priority = '23'
            elif chrom == 'Y':
                priority = '24'
            elif chrom == 'MT':
                priority = '25'
            else:
                priority = '26'
    
    return priority