Origins of Variation in Genomes Flashcards
What are the difference between mitosis and meiosis?
Mitosis
- somatic cells
- 2n -> 2n + 2n
- genetically identical daughter cells
Meiosis
- haploid gamete production
- 2n -> nx4
- genetically different daughter cells
- includes recombination
What is homologous recombination?
crossing over
occurs in meiosis
breakage and going of DNA
reciprocal
genetic rearrangement
creates new combination of alleles
Non-homologous strand break repair
cells quickly degrade bases around double strand
reform with ligase
Homologous strand break repair
bases around break are degraded to stop overhang
broken area accurately copied across from homologous source
double strand break repair
exonuclease creates 3 overhangs
strand invasion creates heteroduplex structure
D loop moves along copying it
What is heteroduplex formation?
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
repair double strand breaks
break accurately repaired
mutations overwritten
universal process
non-reciprocal
basic mechanism of homologous recombination
How can homologous recombination generate crossovers?
occurs in meiosis
breakage and joining of DNA
reciprocal
genetic rearrangement
2 D loops are generated instead of 1
What is a Holliday junction?
4 double stranded arms joined in a square at the centre
What is linkage analysis?
Genes on chromosomes are linked physically and genetically
the further apart the linked genes are, the higher the likelihood of recombination
What is gene targeting?
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
Homologous recombination in bacteria
bacteria don’t undergo meiosis
can alter and write more useful DNA
can edit out genes but double crossing over
Homologous recombination in bacteriophage
bacteriophages are bacterial viruses
create new versions of bacteriophages
creating recombinant phage within the bacteria