Foreword

To start, put yourself in a hypothetical situation: you have an identical twin brother who was secretly transferred to another family when you were less than a year old. His new family was poor, and your family was rich and therefore the environment in which you grew up was much better than his. After 50 years, by chance, you both happen to meet and it turns out that you look quite different from one another and are in different states of health; he is short and is suffering from heart disease, while you are tall, healthy, and are training to run a marathon. So, what was it that made you two so different, in light of the fact that your genetic materials are completely identical?

Long-interspersed nuclear elements (LINEs) are genetic components found in higher eukaryotes. They are retrotranposons, meaning that they are transcribed into mRNA and then translated into proteins that act as a reverse transcriptase. The reverse transcriptase makes a copy of the LINE DNA which can then be integrated into the genome at a new site. The only active LINE in humans is LINE-1. It has been associated with oncogenesis and Haemophilia A, a diseased caused by insertional mutagenesis.