Transposons

Question 1

What are transposable elements?

Answer 1

-able to move from one location in a chromosome to another, or to a different chromosome
-leads to chromosome breakage and insert into new location (mutations)

Question 2

How do transposons insert into chromosomes?

Answer 2

1. create staggared breaks in target DNA
2. transposon attaches to single stranded ends
3. DNA replicated at gaps, creating flanking direct repeats

Question 3

What is the transposase enzyme and terminal inverted repeats?

Answer 3

transposase enzyme: makes staggared break in DNA

terminal inverted repeats: inverted and complimentary, found at ends of transposons

Question 4

What are the two classes of transposons?

Answer 4

Class I: Retrotransposons

-RNA transcribed from transposon (DNA)
-DNA copy made from RNA by reverse transcription and inserted into new chromosomal site

Class II: DNA transposons
1. Non-replicative: cut and pasted into new site
2. Replicative: copy and pasted into new site

Question 5

What mechanisms are used to control or limit transposition

Answer 5

1. DNA methylated, suppresses transcription and production of transposase enzyme
2. alterations in chromatin structure, prevents transcription
3. control of transposase translation by piRNAs that bind to piwi proteins and inhibit translation of transposase mRNA

Question 6

Mutagenic effects

Answer 6

Pairing of looping and crossing over between two transposable elements in same direction leads to deletion

pairing by bending and crossing over between two transposons in opposite direction leads to inversion

mispairing leads to duplicaiton in one sister chromatid and deletion in another

Question 7

two major groups of transposable elements in bacteria

Answer 7

1. simple transposable elements: carry only required info

-insertion sequence
-has transposase gene
-has terminal inverted repeats
-flanked by direct repeats at target site

2. Complex: carry extra DNA

composite:
-any sequence flanked by two simple transposable elements
-flanked by two direct repeats

non-composite:
-has transposase gene
-has terminal inverted repeats

Question 8

Ac and Ds elements in corn

Answer 8

mosaic colouring caused by 2 unstab;e genes

Ac: activator gene
-contains terminal inverted repeats
-transposase gene
-autonomous transposition

Ds-dissociation gene
-inactivated transposase gene
-requires transposase Ac to transpose
-nonautonomous transposition

Question 9

Hybrid Dysgenesis

Answer 9

-repressor protein inhibits transposition, incorporated into cytoplasm of the egg of a p+ female
-not carried in sperm
P-/P+ male x P+ female=normal
P+ male x P- female= mutant

Question 10

SINES and LINES

Answer 10

SINES

-Alu most common transposon in humans
-arose from RNA intermediate
-have short flanking repeats when sequences inserted into DNA

LINES

-have shortened sequences but longer than SINES