Final answer:
Reversible termination in Illumina sequencing by synthesis is a method known as the dideoxy chain termination method. It involves the use of chain terminators called dideoxynucleotides (ddNTPs) that prevent further extension of the DNA strand. This method allows the generation of DNA fragments of different sizes.
Step-by-step explanation:
The role of reversible termination in Illumina sequencing by synthesis is to generate DNA fragments of different sizes. This method is also known as the dideoxy chain termination method. It involves the use of chain terminators called dideoxynucleotides (ddNTPs) which lack a free 3' OH group. When a ddNTP is added to a growing DNA strand, the chain cannot be extended further. By using a predetermined ratio of deoxynucleotides to ddNTPs, DNA fragments are produced that terminate at different points during replication.