THE NON-RANDOM DISTRIBUTION OF INVERSION BREAKS IN THE MIDGE TENDIPES DECORUS

Abstract

The midge Tendipes decorus shows a high degree of chromosomal polymorphism, almost exclusively in the form of paracentric inversions. Inversions are significantly concentrated in the second chromosome, to which 54 of the 70 analyzed breaks are assigned. Within this chromosome, inversion breaks are again grouped in a number of clusters. Successive inversion steps frequently show near-coincidence of breaks and sometimes strict coincidence, so that near-tandems and tandem complexes result. The causes of the non-random distribution of breaks are discussed. The hypothesis first proposed by Novitski is favored: that inversion heterozygosis as such predisposes to the formation of derivative inversions related in one or more breaks to the antecedent.