A test for equilocality of supernumerary heterochromatin distribution in grasshoppers

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Abstract
The presence of extra segments in four or more nonhomologous chromosome pairs led us to test the applicability of the principle of equilocality of heterochromatin distribution to supernumerary heterochromatin. In Chorthippus brunneus, which carries extra segments on all chromosomes except the L3, the 13 heterochromatic variants occupy all possible locations with 3 proximal, 5 interstitial, and 5 distal. This indicates that equilocality does not seem to apply to the supernumerary heterochromatin in this species. On the other hand, the four extra segments found in Chorthippus parallelus and five of the seven extra heterochromatic segments found in Chorthippus binotatus are all located distally on the M5-S8 chromosomes. Thus for these groups of chromosomes the extra heterochromatic segments do appear to show a tendency for an equilocal distribution.