Mitochondrial bottlenecks slow down the rate of Muller’s ratchet. Asymmetric transmission and bottlenecking are two complementary strategies of increasing the cell-to-cell variance and ameliorating the mutational meltdown. Tight mitochondrial bottlenecks increase cell-to-cell variability in mutation load and the efficacy of purifying selection at the level of mitochondrial group, and slow down the irreversible accumulation of deleterious mutant alleles (A,C), countering the deleterious effects of paternal leakage (B,D). On the other hand, bottlenecks also increase clonality of mitochondrial genome within the cell, rendering homologous recombination less effective (A, C). L = 1 (A), L = 5.0 (C), µ = 0.005, N = 500, M = 20, R = 0 in (B) and (D), and C = 1.