Repetitive DNA Part 4 Flashcards
Transposition
- moves mobile genetic elements between non homologous sites in the genome
1) to different places within one chromosome
2) between 2 chromosomes
what is responsible for a large fraction of the evolutionary change in a genome
- mobile elements
each mobile element contains
- an enzyme that mediates its own movement - transposase
- special sites upon which the enzyme acts - to mobilize the transposons
transposons
- transposable elements
mobile genetic elements target site selectivity
- have only little target site selectivity therefore move freely throughout the genome
transposase acts on specific DNA sequence at the end of transposon
- disconnects transposon from flanking DNA
- inserts it into new target DNA site
- no requirement for homology
- most move only rarely
3 classes of transposons
- DNA transposons
- LTR-containing transposons
- non-LTR retrotransposons (non autonomous retrotransposons)
wild type maize
- C locus expressed
Mutated maize
- transposable element ds is inserted into C locus and knocked out its expression
reverted maize
- Ac acts upon Ds element to jump it out in some cells to restore color
which element is more active
- Ac element more active than Ds element
Ac transposon
- has full transposon
- has transposase
- inverted repeats
transposase acts on Ds
- to move them but they can’t move themselves
original mutation
- result of transposable element in C gene
- DS
another transposable element
- Ac = activator
- induces Ds to transpose out of C, causing reversion
Ds can transpose, but
only with the help of Ac
Ac autonomous transposon
- can transpose itself and inactivate other Ds genes by itself
DNA transposons move in the genome by
- cut and paste mechanism
two pathways of cut and paste transposons
- replicative
- nonreplicative
replicative
- copy self and leave old copy in place
- 2 copies now
nonreplicative
- jumps from one place to another
retrotransposons
- move by copy and paste mechanism
copy and paste
- makes RNA intermediate that must be reverse transcribed into DNA before being inserted into the genome
LTR-containing retrotransposons
- similarities with retroviruses
- AIDS virus, HIV infects human cells
how HIV replicates
- take viral RNA and using host nucleotides converts viral RNA into ssDNA then transcribed into dsDNA
non-LTR retrotransposons
- movement requires reverse transcriptase
- move by a copy and paste mechanism
types of non-LTR retrotransposons
- LINEs
- SINEs
80% of maize genome
- retrotransposons
half the genome of humans is composed of
- repetitive DNA
