Question

8a). What general characteristics are found in many transposable elements?

8b). How does a retrotransposon move?

8c). Research has shown that more mutations accumulate in regions of the chromosome that consist of compact chromatin, such as heterochromatin. Offer an explanation for why mutation rates would be higher when chromatin is more compact.

Answer 1

8a) They are seen abundant in eukaryotes.They are source of repetitive DNA.

Can induce structural , regulatory or both changes in the same organism.

They can adopt either cut and paste mechanism or copy paste mechanism.

Cannot replicate apart from host chromosomes.

Transposition don't require extensive areas of homology - Random movement.

Site specific recombination dependent on the inserted areas.

Transposase coded by the transposase genetic elements mediates transposition.

8b) Retro transposons move by copy paste mechanism but here the copy is RNA instead of DNA. Retrotransposon undergoes transcription to produce it's RNA. This RNA is converted to DNA by reverse transcriptase enzyme. This DNA is incorporated in to another site of the genome.

8c)

In heterochromatin regions, most of the cytosines are methylated. This high methylation rate can lead to oxidation to form a different base. For example methylated cytosine is converted to thymine after oxidation.

Heterochromatin is really condensed, there for it forms loops to interact with the active DNA. This loop formation can enhance various large scale deletions.

These condensed regions has lot of repetitive DNA, insertion and deletion of these repetitive DNAs can lead to large scale mutations in heterochromatin.

This highly condensed regions are less accessible to DNA repair enzyme. With no surveillance at all, the mutations keep accumulating.