MALE-STERILITY AND DOUBLE HETEROZYGOSITY FOR CHROMOSOMAL INVERSION

A meiotic analysis has been carried out on male mice heterozygous for one of two inversions in Chromosome 2, In(2)5Rk and In(2)2H, as well a s on double heterozygotes for these two overlapping inversions. Electr on microscopic observation of synaptonemal complexes revealed that het erosynapsis had occurred in a large number of spermatocytes, producing a small number of cells with an inversion loop. Heterozygous carriers of a single inversion loop reproduced quite normally, whereas doubly heterozygous carriers of a double loop showed a reduction in spermatog enesis. These data shed new light on the role of inversions in speciat ion.