‘sticky’ ends

 A restriction enzyme can cut DNA at a specific sequence of nucleotides usually 4, 6 or 8 nucleotides long. This may produce either "blunt" ends or "sticky" ends. A "sticky" end is produced when the restriction enzyme cuts at one end of the sequence, between two bases on the same strand, then cuts on the opposite end of the complentary strand. This will produce two ends of DNA that will have some nucleotides without any complentarty bases. A restriction enzyme will only cut at a specific sequence, and since DNA is palindromic the end of one sequence is the same as the opposite end of the complementary sequence.