A TEST FOR ADAPTIVE CHANGE IN DNA-SEQUENCES CONTROLLING TRANSCRIPTION

Spatial and temporal differences in gene expression in early developme nt result from the interaction of transcription factors with enhancer and silencer sequences in DNA. The evolution of the developmental proc ess thus involves changes in the DNA sequences that bind transcription factors. Here we advocate a non-parametric statistical test - compari ng levels of polymorphism and fixed substitutions between species - to look for evidence of adaptive evolution in sequences controlling gene expression. The test is illustrated by DNA sequence changes in the pr oximal part of the 'zebra' element in the fushi terazu gene of the Dro sophila melanogaster species group, which yield significant evidence f or adaptive substitutions. (This is despite highly significant evidenc e that all parts of the sequence have been subject to strong selective constraint.) The test can be applied generally to investigate adaptiv e evolution in the control of gene expression.