On Fourth Chromosome Lethals from a Natural Population of Drosophila melanogaster

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Abstract
An analysis of 104 fourth chromosomes removed from a wild population of D. melanogaster near Powell, Tennessee, revealed three containing recessive lethal genes. These microchromosomal lethals are all non-allelic. Their inability to produce pseudodominanee effects with any of the known recessive visibles on chromosome four makes it unlikely thay they are deficiencies for these loci. Two of the Powell lethals proved identical to two different lethals of X-ray origin, and a third interacted lethally with ben-Dominant, one of the six dominant visibles tested. These observations support the idea that there are very few sites in the small autosome capable of harboring a lethal allele. Although the data are not extensive, they suggest that microchromosomally based lethals may be carried in gene pools of natural populations at a frequency higher than one would expect considering the paucity of loci in this autosome. Future investigations, enlarged in scope and improved methodologically, will be undertaken to test this hypothesis.