tandem array Repetitive DNA, where the repeating units are contiguous. Some genes of high copy number occur in tandem arrays e.g. ribosomal DNA in eukaryotes). Satellite DNA is also often arranged in tandem arrays. Such DNA regions are prone to the genetic processes of unequal crossing over and replication slippage.

tandem array (in genetics) A series of copies of a gene arranged in tandem along a chromosome. Nucleolar organizers, for example, can contain up to 250 copies of a single ribosomal RNA (rRNA) gene in tandem. Genes for histone proteins also occur in tandem arrays. Such arrays ensure that large amounts of the gene product are synthesized by the cell.