dideoxy DNA sequencing

    Replication of the DNA strand in a sequencing reaction begins with (A) a set of primed template ssDNA molecules, and all four dNTPs plus one (B) ddNTP, in the example ddATP. The -H on the 3'-C prevents further extension. (C) The region to be sequenced includes three T positions. The ddATP is randomly incoporated during strand synthesis, such that chain growth terminates at each T where a complementary ddA has been incorporated.  Four separate reactions with each of the four ddNTPs produces a complete set of fragments that differ by plus or minus one nucleotide over the entire length of the template DNA..

Figure © 2012 TA Brown, Introduction to Genetics (1st ed.); additional text © 2012 by Steven M. Carr