Which classes of endogenous retroelements are known to date?
['Transposons are divided into two general classes based on their transposition intermediate (DNA or RNA). Only one subclass, the non-LTR retrotransposons, which includes the Long INterspersed Element-1 (LINE-1 or L1), is currently active in humans as indicated by 96 disease-causing insertions', 'Diversity of LTR-retrotransposons and Enhancer/Suppressor Mutator-like transposons in cassava', 'Members of two classes of LTR-retrotransposons, Ty1/copia-like and Ty3/gypsy-like, and of Enhancer/Suppressor Mutator (En/Spm)-like transposons were isolated and characterised', 'Mammalian LINE-1 (L1) elements belong to the superfamily of autonomously replicating retrotransposable elements that lack the long terminal repeated (LTR) sequences typical of retroviruses and retroviral-like retrotransposons']
['Endogenous retroelements fall into two distinct classes: retrotransposons containing LTRs (Long Terminal Repeats), and retrostransposons lacking LTRs.']
['retrotransposons containing LTRs (Long Terminal Repeats)', 'retrostransposons lacking LTRs (Long Terminal Repeats)']