Copies throughout genome. Used to identify human sequences in hybrid cells. SL signal recognition particvle RNA deleted version. Needs revesre transcription to move. G band, L1 is R-band.
Different genes operate at different times.
Duplication by unequal C-O, followed by evolution of a useful function or mutational loss 2. Has poly-A tail and no introns, often lacking variable part of 5' end. RT found in retroviruses and retrotansposons. Some of these e.g. L1 are from the retrotransposon itself, others are from any cellular gene. Normally RT not found in cells, but apparently it is occasionally active.