STUDY QUESTIONS: LEC 16-17
1. What are potential effects of transposons on the genome?
Insertion may cause mutation
Protein product of L1 element may create DNA DSBs. Alternatively, existing DSB may be repaired
by non-classical insertion of a retrotransposon
Gene conversion may alter sequence compositions of homologous retrotransposon copies
Insertion associated with deletion of target genomic sequence
Ectopic recombination between non-allelic homologous retrotransposons may result in genomic
rearrangements e.g., deletions or duplications
2. List and briefly describe three mechanisms used by genetic elements to randomly move from
one site in the genome to another.
DNA-only transposons - Example: insertion sequence (IS) elements: Encode only genes for
mobilization and insertion (host replication machinery used for replication).
Retrotransposons (retroviral-like) carry long terminal repeat sequences (LTRs) and two genes
important for recombination (RT and integrase). Cannot move from cell to cell; move only to
new DNA within the cell.
Nonretroviral retrotransposons or polyA retrotransposons: - poly A at 3â end of RNA transcript;
5â end often shortened. Moves via RNA intermediate that is often produced from a neighboring
promoter. Can be autonomous e.g., LINEs (long-interspersed sequences) or nonautonomous
e.g., SINEs (short-interspersed sequences)
3. Draw a fully annotated diagram illustrating the transposition mechanism of a simple IS
transposon (or retroviral-like retrotransposon, or non-retroviral retrotransposon).
4. Who was Barbara McClintock and what was her major scientific contribution (no more then
Barbara McClintock won the Noble Prize in physiology and medicine in 1983 for her discovery of
mobile genetic elements. Through her studies on corn, she discovered and published
information on transposable elements and their role in mutating genes.
5. What are LINEs and SINES? What is the major difference between them?
LINEs ï long interspersed sequences; code for proteins necessary to reverse transcribe and