The chance of fixation of a reciprocal translocation in a population of plants, with exclusive sexual reproduction, is of the order 10-3 if the effective population number (N) is 10. It is of the order of 2 x 10-6 in groups of 20 individuals and of the order 3 x 10-14 in groups of 50 individuals. It is assumed that the heterozygotes are semisterile, and that there is no compensating advantage in semisterility by reduction of competition among the progeny and that the translocation has no advantage per se. These figures may be compared with 1/2N, the chance of fixation of an indifferent mutation. Reciprocal translocations in animals have a slightly better chance of fixation than in plants in populations of the same effective size, even if only the balanced types are viable and fertile. Cases in which the heterozygous unbalanced type are at no disadvantage in viability and in number of gametes produced, only the homozygous deficiencies being eliminated, have considerably better chances of fixation than in t...