NOTE 17K: This formula differs from that for additive selection or for selection on haploids (Box 28.2) by the extra term (1/p0) – (1/p1). If the initial frequency is very small (p0 = 10–6, say), then this is far larger than the last logarithmic term (1/p0 = 106, but log(1/p0) = 13.8). Because a recessive allele is rarely exposed to selection when it is rare, it takes a very long time to increase from low frequency.