def adjust_genotype(sample_call, alt_index, allele_symbol = '-'):
    """
    Adjust genotype fields by alternative allele index

    Args:
        sample_call (pyvcf CALL): sample call pyvcf record
        alt_index (int): Alternative allele index
        allele_symbol (str): replacment genotype symbol for overlapping variants
    Returns:
        gt_data (dict): Adjusted gt data

    """
    gt_data = {}
    for genotype_field in sample_call.data._fields:
        if genotype_field == 'GT':
            gt = sample_call[genotype_field].split('/')
            ref = allele_symbol
            alt = allele_symbol
            if gt[0] == gt[1]: #hom call
                ref = '1'
                alt = '1'
            else: #het call
                if (int(gt[0]) == alt_index + 1 or int(gt[1]) == alt_index + 1):
                    alt = '1'
                if (int(gt[0]) == 0 or int(gt[1]) == 0):
                    ref = '0'
            gt_data['GT'] = '{0}/{1}'.format(ref, alt)

        elif genotype_field == 'AD':
            gt_data[genotype_field] = [sample_call[genotype_field][i] for i in [0,alt_index+1]]
        else: # Correct other (all) entries for alt index!
            gt_data[genotype_field] = sample_call[genotype_field]

    return gt_data