Detour: Repeats in the Human Genome

Transposons

A transposon is a DNA fragment that can change its position within the genome, often resulting in a duplication (repeat). A transposon that inserts itself into a gene will most likely disable that gene. Diseases that are caused by transposons include hemophilia, porphyria, Duchenne muscular dystrophy, and many others. Transposons make up a large fraction of the human genome and are divided into two classes according to their mechanism of transposition, which can be described as either retrotransposons or DNA transposons.

Retrotransposons are copied in two stages: first they’re transcribed from DNA to RNA, and the RNA produced is then reverse transcribed to DNA by a reverse transcriptase. This copied DNA fragment is then inserted at a new position into the genome. DNA transposons don’t involve an RNA intermediate but instead are catalyzed by transposases. The transposase cuts out the DNA transposon, which is then inserted into a new site in the genome, resulting in a repeat.