def jukesCantorD(p, L=100):
    """
    >>> jukesCantorD(.1)
    (0.10732563273050497, 0.001198224852071006)
    >>> jukesCantorD(.7)
    (2.0310376508266565, 0.47249999999999864)
    """
    assert 0 <= p < .75

    rD = 1 - 4. / 3 * p
    D = -.75 * log(rD)
    varD = p * (1 - p) / (rD ** 2 * L)

    return D, varD
>>> jukesCantorD(.1)
    (0.10732563273050497, 0.001198224852071006)
    >>> jukesCantorD(.7)
    (2.0310376508266565, 0.47249999999999864)