Chapter 20 Transposable Elements

1. Transposable elements are divided into two classes on the basis of their mechanism for movement: a. Some encode proteins that move the DNA directly to a new position or replicate the DNA to produce a new element that integrates elsewhere. This type is found in both prokaryotes and eukaryotes. b. Others are related to retroviruses, and encode reverse transcriptase for making DNA copies of their RNA transcripts, which then integrate at new sites. This type is found only in eukaryotes. 2. Transposition is nonhomologous recombination, with insertion into DNA that has no sequence homology with the transposon. a. In prokaryotes, transposition can be into the cell’s chromosome, a plasmid or a phage chromosome. b. In eukaryotes, insertion can be into the same or a different chromosome. 3. Transposable elements can cause genetic changes, and have been involved in the evolution of both prokaryotic and eukaryotic genomes. Transposons may: a. Insert into genes. b. Increase or decrease gene expression by insertion into regulatory sequences. c. Produce chromosomal mutations through the mechanics of transposition