G3

Question 1

Why is deleted fragment of a chromosome lost in cell divsion?

Answer 1

because it does not contain a centromere so cannot be pulled to poles

Question 2

What is an intragenic deletion and its affects and how it can be distinguished from a point mutation

Answer 2

deletion within a gene
has the same affect as a null mutation
distinguished from point as doesnt revert to wildtype

Question 3

what is an example of a viable homozygous null mutation

Answer 3

human albinism

- if homozygous null mutation is viable than deletion will be too

Question 4

what is a multigenic deletion and what affect does it have on a homozgote or heterozygote

Answer 4

several genes are missing - serious consequences
if homozygous by inbreeding, lethal
may be lethal for heterozygote

Question 5

what can a multigenic deletion uncover

Answer 5

deleterious recessive alleles, allowing single copies to be expressed

Question 6

what can lethality of large heterozygous mutations be explained by

Answer 6

gene imbalance and expression of deleterious recessives

Question 7

where can deletion loops be found, what are they and what can they tell us

Answer 7

polytene chromosomes in drosophillia melangaster
failure of normal homologs to pair creates a deletion loop
deletions can be allocated to specific location by determining position of loop

Question 8

what is pseudodominance and what can we detect from this

Answer 8

when recessive allles appear to have dominance due to deletion in other homolog
- can detect deletions from this

Question 9

What is deletion mapping

Answer 9

when each deletion is paired with each mutant under test and the phenotype observed to see if the mutation is pseudodominant - able to poinpoint location of mutant
if pseudodominant deletion and mutation in same region
if deletetion location of know can be applied in the reverse to map assess position of mutant alles

Question 10

what is cri du chat syndrom

Answer 10

caused by heterozygous deletion at tip of short arm chromosome 5, low fatalty rates

Question 11

What are tandem duplications

Answer 11

2 adjacent identical dna seqs or chromosome segments can be seen in drosophilia polytene chromosome - rare in humans

Question 12

what is an exammple of humans homoxygous for duplication

Answer 12

case unknown

Question 13

what are insertional duplications

Answer 13

identical dna seqs of chromosomes segements that are in different locations of a chromosome or in different chromosomes - KEY TO EVOLUTION

Question 14

Describe Class 1 transposons

Answer 14

reteroelements
move by retrotransposition
high copy number possible as several RNAs can be transcribed froma s ingle class 1 element.
permenant transposition

Question 15

describe class 2 transposons

Answer 15

named DNA elelmetns
move from one site to another - excise from donor site
if insertion of a gene has created a mutation, excision leads to the reversion of orginal mutation

Question 16

give an example of class 1 and class 2 transposons

Answer 16

class 1 = alu element
class 2- discovered in maize leads to spotted kernels due to their excision from genes expressing pigmentq

Question 17

what are mendels wrinkled peas an example of

Answer 17

a wildtype round R allele interuptted by a transposon. `

Question 18

how much of human mouse and drosophilia genome are transposons
n

Answer 18

human and dros = 50%

mouse =70%

Question 19

What are bacterial insertion sequences?

Answer 19

prokaryotic transposons
segements of bacterial DNA that move from one position toa different position on the same chromosome
block expression of other genes in same operon if these genes are downstream from the promoter

Question 20

What are the two types of bacterial insertion sequences

Answer 20

complex/composite and simple

Question 21

describe complex/composite transposons

Answer 21

contain several genes between 2 IS orientated at opposite sides of bacterial genes.
enzyme transposase encoded by IS element catalysed movement.
IS element that makes up composite transposons cannot transpose on their own

Question 22

give an example of a complex transposon

Answer 22

Tn10 carries a gene that confers resistance to tetracycline and is flanked by two IS10 elements in opposite orientations.

Question 23

Describe simple transpososons

Answer 23

flanked by IR sequences which are short and dont encode transposase enzyme
tranposase is encoded within genes in addition to bacterial genes.

Question 24

how were P elements in drosophilia discovered

Answer 24

found in natural but not lab grown

occured in last 70 years

Question 25

Describe RNA interferance/silencing

Answer 25

dsRNA are processed by DICER, into siRNAs of 21 bps, resulting siRNAs bind to argonaut (Ago) protein to form silenecing complex
siRNA Ago cleaves the target transcript - silencing the gene
main way of silencing for tranposable elements in germ line

Question 26

What are the 5 members of the argonaut family in Drosophilia?

Answer 26

Ago1, Ago2, Ago4, ad the PIWI subfamily - Piwi and Aubergine (Aub)

Question 27

What do PIWI family members do

Answer 27

associate with piRNAs

Question 28

what are piRNAs

Answer 28

PIWI interacting RNA

in dros = 23-30nt long ssRNA that mainly original from transposable elements

Question 29

What is an M cytotype

What is a P cytotype

Answer 29

M =lab stocks

P= natural stocks

Question 30

what happens when you cross M female with P male

Answer 30

offspring show different phenotypes

sterility - high mutation and high freq of chromosomal aberration = dysgenic offspring

Question 31

what happens when you cross P female with M male

Answer 31

non dysgenic offspring produced

Question 32

What are wild females of D.melanogaster thought to contain that lab grown do not?

Answer 32

repressor that prevents transposase transcription found in cytoplasm of oocyte.
which reduces disruption to genome caused by P elements allowing fertile progeny

Question 33

What is hybrid dysgenesis and what is it marked by

Answer 33

dygenesis of offsping produced by M mother and P father. marked by temp depepndent sterilty and elevated mutation rates as well as increased chromosome rearragment and recombination

Question 34

What part does Aub play in P female mating of d. melanogaster

Answer 34

aub is the PIWI protein that identifies Ptranposon mRNA in early embryo and cuase aub dependent destabilisation.

Question 35

what are lines

Answer 35

retrotransposons that move by reverse transcription

Question 36

what are sines, give an example

Answer 36

dont produce own reverse transcription so rely on sines. examples is ALU

Question 37

Why does tranpostion of P element only occur in germline cells

Answer 37

because splicing event needed to make transposase mRNA doesnst occur in somatic cells