In human In the first human genome draft the fraction of LINE<unk> s of the human genome was given as 21% and their copy number as 850,000. Of these, L1, L2 and L3<unk> s made up 516,000, 315,000 and 37,000 copies, respectively. The non-autonomous SINE<unk> s which depend on L1<unk> s for their proliferation make up 13% of the human genome and have a copy number of around 1.5 million. They probably originated from the RTE family of LINEs. Recent estimates show the typical human genome contains on average 100 L1<unk> s with potential for mobilization, however there is a fair amount of variation and some individuals may contain a larger number of active L1<unk> s, making these individuals more prone to L1-induced mutagenesis. Increased L1 copy numbers have also been found in the brains of people with schizophrenia, indicating that LINE<unk> s may play a role in some neuronal diseases. Mechanism of target-primed reverse transcription (TPRT), directly at the site of integration: L1 RNP recognize AAAATT hexanucleotides and ORF2 endonuclease activity cleaves the DNA first-strand. L1 polyA tail associate with TTTT overhang and the host DNA is used as a primer to initiate reverse-transcription. ORF2 probably also mediate second-strand cleavage and attachment of newly synthesized cDNA to the DNA template, using again host DNA as a primer for second-strand synthesis.
Long interspersed nuclear element
TRNA 
CccDNA
Gene
Replicon 
Cis-regulatory element
Insertion sequence
Exosome 