Frequencies of Second and Third Chromosome Lethals in a Tropical Population of Drosophila melanogaster

Using a genetically-marked, translocation stock that balances second and third chromosomes simultaneously, 95 "genome" lethals were recovered in 119 tests of material from Bogota, Colombia (80% lethals). Eighty six of 89 tested resulted from lethals which could be located as follows: 18 were on the second alone, 31 on the third alone, and 37 were on both the second and the third. The remaining three genome lethals were caused by combinations of second and third chromosomes with individual deleterious effects too small to qualify as either lethal or semilethal. Of the lethals that were located on definite chromosomes, 55 were on the second and 68 were on the third; this does not differ significantly from a 1: I distribution. Consequently, the frequencies of lethal second and third chromosomes in the Colombia population appear to be similar at about 55 % each