In support of the long-held idea that cone ratio is genetically determined by variation linked to the X-chromosome opsin gene locus, the present study identified nucleotide differences in DNA segments containing regulatory regions of the L and M opsin genes that are associated with significant differences in the relative number of L versus M cones. Specific haplotypes (combinations of genetic differences) were identified that correlated with high versus low L:M cone ratio. These findings are consistent with the biological principle that DNA sequence variations affect binding affinities for protein components of complexes that influence the relative probability that an L versus M opsin gene will be silenced during development, and in turn, produce variation in the proportion of L to M cones.

DNA replication in the spermatogonial cells of Schistocerca gregaria and Gryllotalpa fossor has been analysed. This study has demonstrated the presence of at least two discrete populations of spermatogonial cells in both the insects with different intermitotic timings. The replication pattern of the sex chromosome in Schistocerca seems to be dependent on the pycnosity status, whereas, in Gryllotalpa, it is independent of the condensation pattern.