25. Effects of retrotransposons on mammalian genomes

Mammalian genome evolution has in large part been driven by retrotransposons. In previous chapters, I’ve discussed our work on the 17–20% of mammalian genomes that are L1 sequence, mostly L1 remnants. Another 10–12% of those genomes are repeat sequences, such as Alu elements, that have been inserted into the genome by retrotransposition using the L1 endonuclease and reverse transcriptase. Both L1 and Alu elements have a substantial effect on the evolution of genomes. I’ve mentioned the L1 insertions in humans that occur at a rate that is still unknown, but recent estimates place it between 1 in 100 and 1 in 150 individuals. Alu insertions are more frequent, occurring at a rate of roughly 1 ...

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