1. A system to replicate or globally replicate one or more nucleic acid species in a sample, the system comprising: (a) a random extender unit comprising a polynucleotide with a 3′ random primer sequence and a 5′ first universal sequence; wherein the first universal sequence is not complementary to the target nucleic acid species in the sample, and wherein the first universal sequence is selected from the group consisting of: SEQ ID NOs: 1, 2, 3 and 4, and wherein the 3′ end of the population of random extender units is blocked, wherein said block is not thermally removable; and (b) a first universal primer comprising the first universal sequence.