Origins of Variation in Genomes

Question 1

What are the difference between mitosis and meiosis?

Answer 1

Mitosis
- somatic cells
- 2n -> 2n + 2n
- genetically identical daughter cells

Meiosis
- haploid gamete production
- 2n -> nx4
- genetically different daughter cells
- includes recombination

Question 2

What is homologous recombination?

Answer 2

crossing over
occurs in meiosis
breakage and going of DNA
reciprocal
genetic rearrangement
creates new combination of alleles

Question 3

Non-homologous strand break repair

Answer 3

cells quickly degrade bases around double strand
reform with ligase

Question 4

Homologous strand break repair

Answer 4

bases around break are degraded to stop overhang
broken area accurately copied across from homologous source

Question 5

double strand break repair

Answer 5

exonuclease creates 3 overhangs
strand invasion creates heteroduplex structure
D loop moves along copying it

Question 6

What is heteroduplex formation?

Answer 6

synapsis
binds to 3’ single stranded end of damaged DNA
forms structure and searches for homology
unzips source of DNA and generates a heteroduplex structure
called a D loop

Question 7

repair double strand breaks

Answer 7

break accurately repaired
mutations overwritten
universal process
non-reciprocal
basic mechanism of homologous recombination

Question 8

How can homologous recombination generate crossovers?

Answer 8

occurs in meiosis
breakage and joining of DNA
reciprocal
genetic rearrangement

2 D loops are generated instead of 1

Question 9

What is a Holliday junction?

Answer 9

4 double stranded arms joined in a square at the centre

Question 10

What is linkage analysis?

Answer 10

Genes on chromosomes are linked physically and genetically

the further apart the linked genes are, the higher the likelihood of recombination

Question 11

What is gene targeting?

Answer 11

introducing specific DNA in vivo
containing homologous sequences and selectable markers
recombination leads to the integration of DNA

can either be a single crossover and split the gene
or double and remove the gene completely

Question 12

Homologous recombination in bacteria

Answer 12

bacteria don’t undergo meiosis
can alter and write more useful DNA
can edit out genes but double crossing over

Question 13

Homologous recombination in bacteriophage

Answer 13

bacteriophages are bacterial viruses
create new versions of bacteriophages
creating recombinant phage within the bacteria