Double ended sequencing

A method of sequencing a nucleic acid molecule comprising:

• (a) hybridizing a first unblocked sequencing primer to a first strand of the nucleic acid molecule;
• (b) hybridizing a second blocked sequencing primer to a second strand of the nucleic acid molecule;
• (c) incorporating at least one base onto said first strand by extending said first unblocked primer with a polymerase;
• (d) preventing further elongation of said unblocked primer;
• (e) deblocking the second sequencing primer;
• and
• (f) incorporating at least one base onto said second strand by extending said second primer with a polymerase;
• wherein steps (a) and (b) are performed in any order or simultaneously.

A method of determining a molecular haplotype of a DNA sample at multiple loci comprising the steps of:

• (a) hybridizing 2 or more sequencing primers adjacent to a plurality of loci in a DNA sample wherein all the primers except for one are reversibly blocked primers and wherein each locus contains a nucleic acid sequence that determines a haplotype;
• (b) determining a haplotype at one locus by polymerase elongation from an unblocked primer;
• (c) preventing further elongation of said unblocked primer;
• (d) deblocking one of the reversibly blocked primers into an unblocked primer;
• (e) repeating steps (b) to (d) until all the reversibly blocked primers are deblocked and used for determining a molecular haplotype.