Slipped-strand nucleotide mispairing can generate variation in gene expression. Illegitimate base pairing in regions of repetitive DNA during replication, coupled with inadequate DNA mismatch repair systems, can produce deletions or insertions of repeat units. Bulging in the replicated and template strands gives rise to larger and smaller numbers of repeat units, respectively. The figure shows a strand of DNA (blue) being carried through two rounds of replication.
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All mammals have basically the same set of genes, yet there are obviously some significant differences that distinguish the various species. Recent research suggests that one such difference involves tandem repeats, or short lengths of DNA that are repeated multiple times within a gene. But what, if anything, does having a different number of tandem repeats do to an organism?
