Evolution of the nuclear ribosomal DNA intergenic spacer in four species of the Daphnia pulex complex.

Background: Concerted evolution refers to the pattern in which copies of multigene families show high intraspecific sequence homogeneity but high interspecific sequence diversity. Sequence homogeneity of these copies depends on relative rates of mutation and recombination, including gene conversion and unequal crossing over, between misaligned copies. The internally repetitive intergenic spacer (IGS) is located between the genes for the 28S and 18S ribosomal RNAs.

Evolution of repeated sequences in the ribosomal DNA intergenic spacer of 32 arthropod species.

The evolution of a multigene family (MGF) is affected by the structure and function of its regulatory elements, specifically by the link between recombination and DNA transcription and/or replication. The ribosomal DNA (rDNA) MGF is often hierarchically repetitive, combining function with repetition in a single genic system. Its tandemly repeated operons contain the transcription unit of the 45S ribosomal RNA precursor alternating with an intergenic spacer (IGS) that commonly includes repeated transcription regulatory elements.