The genetic basis of the ‘Assimilated Bithorax’ stock

Summary

• 1. The phenotype of the ‘assimilated bithorax’ stock is due in part to a number of genes, on all the chromosomes, which act directly on the individuals containing them. and partly to a recessive X-chromosome condition which causes a maternal effect.

• 2. Attempts to break down the maternal-effect condition by crossing-over were unsuccessful.

• 3. The maternal effect condition, when made homozygous in a wild-type background, causes the appearance of some bithoraxes in the next generation.

• 4. The condition may have arisen by mutation during the course of the selection by which the assimilated stock was built up, but it may have been present in very low frequency in the initial population.

• 5. The offspring of females homozygous for the maternal-effect condition do not produce a higher percentage of bithoraxes, following ether treatment, than do flies of similar genotype from other mothers.