Processed pseudogenes in Drosophila.

Two species of Drosophila, D. yakuba and D. teissieri, possess pseudogenes of Adh. These pseudogenes lack introns and map to chromosome arm 3R, rather than to chromosome arm 2L, wherein are located the functional Adh genes. Their structure suggests that the pseudogenes arose from reverse transcripts. Because the pseudogenes map to homologous sites in both species, they presumably arose before these species diverged. Remarkably, the pattern of base substitution in the pseudogenes differs between sites that correspond to degenerate and non-degenerate codon positions in their functional paralogs.