def check_missing_genes (DF_results, variants_table):
    """
    Checks which genes didn't appear in the filtered VCF (because there
    wasn't any call). 

    Parameters
    ----------
    variants_table: Pandas Dataframe
        Auxiliary table with information about every position queried
        in the VC.
    DF_results: Pandas Dataframe
        Dataframe where is stored every result of a given sample.

    Returns
    -------
    list_of_genes: List
        List of genes which have to be checked in the unfiltered VCF
    """
    genes_missing = DF_results[DF_results["Result_1"].isna()]
    list_of_genes = []
    for g in genes_missing.index:
        if g in list(variants_table["gene"]):
            list_of_genes.append(g)
    return list_of_genes