Transposable Elements

Question 1

What are transposable elements

Answer 1

strands of DNA capable of jumping from one location in a chromosome to another

Question 2

What is significant about transposable elements

Answer 2

can constitute a significant fraction of the genome
- major source of mutations
- important in the generation of some human diseases

Question 3

What are the common characteristics in transposable elements

Answer 3

• create staggered breaks in DNA
• transposable element attaches to single stranded ends of DNA
• DNA is replicated at the gaps

Question 4

What are flanking direct repeats

Answer 4

3-12bp long
- generated in the process of transposition
- don’t belong to transposable element

Question 5

What are terminal inverted repeats

Answer 5

9-40bp long
- inverted and complementary
- recognized by enzymes called transposase that catalyzes transposition

Question 6

What are the 2 classes of transposons

Answer 6

class 1: retrotransposons (RNA intermediate)
class 2: DNA-transposons-catalyzed by transposase

Question 7

What is a class 1 transposon

Answer 7

DNA copy of element made by reverse transcription from its RNA and inserted into a new chromosomal site

Question 8

What enzyme is required by class 1 transposons

Answer 8

reverse transcriptase

Question 9

What are the two types of class 1 (retrotransposon) transposons

Answer 9

retrovirus (or retrovirus-like) elements and retroposons or retrotransposons

Question 10

Both types of class 1 transposon use ___________ _______________

Answer 10

replicative transpositon

Question 11

What are the two types of class 2 transposons

Answer 11

non replicative transposons and replicative transposons

Question 12

In class 2 of transposons, what are non replicative transposons

Answer 12

element is cut out of one site in the chromosome and pasted into another site
- cut and paste

Question 13

In class 2 of transposons, what are replicative transposons

Answer 13

element is replicated with one copy and is inserted into a new site (but the original remains at its original site)
- copy and paste

Question 14

What mechanisms are in place to control or limit transposition

Answer 14

1. DNA is methylated where transposons are common
2. Alterations in chromatin structure prevent transcription
3. control of transposase translation by piwi-interacting RNAs (piRNA) - bind to piwi proteins an inhibit translation of transposase mRNA

Question 15

Why are transposons considered mutagenic

Answer 15

they can insert themselves in DNA

Question 16

Transposiition is a _______________ mutation

Answer 16

spontaneous

Question 17

What (in relation to transposition) causes hemophilia

Answer 17

insertion of L1 transposable element into blood clotting factor VIII gene

Question 18

What can be the result of a transposon insertion

Answer 18

loss of function mutation - disrupts the coding sequence of a gene
gain of function - activating a nearby gene

Question 19

What is the general end result of transposition

Answer 19

duplications, deletions, inversions, and translocations

Question 20

What does transposition entail

Answer 20

exchange of DNA sequences and recombination

Question 21

Pairing of direct repeats in transposition leads to what

Answer 21

deletion

Question 22

Pairing of inverted repeats in transposition leads to what

Answer 22

inversion

Question 23

Transposable elements in bacteria contain two major groups; what are they

Answer 23

simple and complex transposable elements

Question 24

What are simple transposable elements in bacteria

Answer 24

contain only the information required for movement

Question 25

What are complex transposable elements in bacteria

Answer 25

contain extra DNA not related to transposition

Question 26

What are the subcategories of complex transposons in bacteria

Answer 26

composite and non composite

Question 27

What 2 genes cause the mosaic colouring in corn

Answer 27

Ac-activator gene (transposon) and Ds-dissociation gene (transposon)

Question 28

What are the characteristics of Ac-activator gene

Answer 28

- contains terminal inverted repeats - has transposase gene - autonomous transposition

Question 29

What are the characteristics of Ds-dissociation gene

Answer 29

*similar to Ac - possess inactivated transposase gene - requires transposase from Ac to transpose - non autonomous transposition

Question 30

What are the characteristics of P elements in drosophila

Answer 30

about 2900 bp long - possess inverted repeats - DNA transposon - contains both a transposase and a repressor of transposition

Question 31

By containing both a transposase and a repressor of transposition, what phenomenon is created

Answer 31

hybrid dysgenesis

Question 32

What is hybrid dysgenesis

Answer 32

- occurs when P elements are introduced into. cell that does not have them in its genome - sudden appearance of numerous mutations - chromosome aberrations - sterility

Question 33

What is the mechanism behind hybrid dysgenesis

Answer 33

- repressor protein is a cytoplasmic protein that inhibits transposition - inhibitor is the egg of a female *if a P+ female is crossed with a P- or P+ male, the inhibitor in the egg will prevent transposition and the fly will be wild type *If a P- female was crossed with a P+ male, the lack of inhibitor will allow for rapid transposition leading to mutations an sterility (male does not carry repressor in sperm)

Question 34

What are SINES

Answer 34

short interspersed elements

Question 35

What are LINES

Answer 35

long interspersed elements

Question 36

What is the most common transposable element in the human genome

Answer 36

Alu

Question 37

How much of the human genome is SINES

Answer 37

11%

Question 38

How much of the human genome is LINES

Answer 38

21%

Question 39

How much of spontaneous mutation in drosophila are due to transposition

Answer 39

50%