def split_gens(gens_df, chroms):
    """
    Takes in a gens file with multiple loci, and splits it based on chromosome.
    :param gens_df: gens dataframe.
    :param chroms: list of chromosome notations.
    :return: list of dataframse, each dataframe with one chromosome notation at the CHROM column.
    """
    return [gens_df.loc[gens_df["chrom"] == c] for c in chroms]