Table 2.

Main characteristics of the most abundant retrotransposons [4, 5, 7, 19]

	Retrotransposons (interspersed repeats)—44 % human genome
	Non-long terminal repeat (LTR)		Long terminal repeat (LTR)
Repetitive element	Long interspersed nuclear repeats (LINEs)	Short interspersed nuclear repeats (SINEs)	Endogenous retroviruses (ERV)
Genomic coverage	20 %	11 %	8 %
Features	• L1 is the most abundant class • Autonomous transposons • Reverse transcriptase (RT) encoded by LINE-1	• Alu is the most abundant class • Dependent on LINEs transposable machinery • Mobile polymerase III promoter • 100–400 bp in length	• Reduced transposable activity • Presence of gag and pol viral genes