For example, when changing has the same probability as . Furthermore, nucleotide substitution is subjected to selection which may depend on information contained in only one strand. The leading-strand is copied by a continuous process, while the lagging strand is synthesized discontinuously using multiple, short RNA primers. Additional enzymes are needed to synthesize primers and then later remove them and fill in gaps. Mutagenesis experiments in E. coli have shown that deletions and replication errors are more frequent on the lagging strand.
Differences depend on the agent inducing replication errors.
Excess dTTP causes more errors on the lagging strand, while excess dCTP makes little difference. Chargaff asymmetries in the D. melanogaster Adh region. The expected switch in strand asymmetry occurred across the replication origin. The replication effect was partly obscured by protein-coding sequences which introduce their own bias. No evidence has been found in eukaryotes for replication bias.