What is a palindromic sequence?

A palindromic sequence is a strand of DNA in which the sequence of nucleotides on one rung is repeated, albeit in reverse, on its complementary rung. If the sequence on one side of the double helix reads "GACTG," the complementary side reads "GTCAG."

Many palindromic sequences have been detected in human DNA, as well as the DNA of other organisms, and are thought to be the result of a transcription error in which a section of nucleotides was duplicated, flipped and reattached to the original strand of DNA. Some of these repeat errors have been identified with sites of high mutation in bacteria as well as certain intellectual disabilities in humans.