What causes the elongation of Genome down the evolutionary time line
DNA misreplication events can lead to accidental duplication of DNA (even the entire genome), misalignements in recomibination events, integration of DNA from extracellular sources e.g. viruses. All these events can lead to large scale changes in the genome size of an organisms, smaller scale changes can be insertions and deletions in the DNA from repair pathways such as non homologous end joining.