def m_step(ind_base_prob):
    """
    Update allele frequency.

    Parameters
    ----------

    ``ind_base_prob``: 2d-array like, n x 4 matrix.

    """
    sample_size = ind_base_prob.shape[0]
    expect_allele_prob = ind_base_prob.sum(axis=0) / sample_size
    return expect_allele_prob
