Distribution of lethal genes and their allelism in the O chromosome of Drosophila subobscura

The lethal balanced strain Va/Ba is the only tool available for analysing t he lethal genes on the O chromosome of Drosophila subobscura a. This strain presents the X-ray-induced inversions OVIII+210 and the naturally occuring O3+4. Recombination is possible if wild chromosomes carry the O3+4 arrange ment without any other overlapping inversion. Loukas ei ai. (1980) develope d a mathematical method to standardize all of the types of wild lethal chro mosomes. Although this method has proved useful. results are sometimes anom alous. Here the method is analysed and possible solutions to these anomalie s are suggested.