Genome editing

Question 1

Crispr-Cas9 system

Answer 1

Discovered as a genetic mechanism of acquired immunity which exists in bacteria to combat viral infection

Scientists have recently been able to manipulate the system to perform precise genome edits very efficiently in mammalian genomes

Question 2

how Crispr works in bacteria

Answer 2

bacteriophage DNA segments are inserted into bacteria in between CRISPR repeats which are expressed as hairpin structures. Crispr repeats cut up into monomers with bits of viral DNA attached known as guide RNA.
When the same virus infects again, the crRNAs bind to specialized proteins known as Cas proteins.This CRISPR-Cas complex scans and recognizes the viral DNA, effectively targeting it for destruction.
Once the viral DNA is identified, the Cas proteins cleave the DNA, breaking it apart and preventing the virus from replicating.

Question 3

Crispr-Cas9 application

Answer 3

synthetic guide RNA created to match target mutant DNA that directs Cas9 enzyme to a specific location in the genome. Cuts both strands of target DNA. cell repairs the cut either by homologous recombination repair. resection of DNA creates single stranded ends. Transfect vector into cell that contains the corrected sequence at higher concentrations instead of the single strands finding homologous chromosome which likely also has mutation.
Polymerase fills in gap with corrected sequence

Question 4

Which system has crispr been characterised in

Answer 4

haematopoietic
moving onto editing germline to prevent inherited disease

Question 5

gene drive

Answer 5

genetic engineering technique that increases the likelihood of a specific gene being inherited, allowing it to spread rapidly through a population. uses Crispr

Question 6

how genetic drive works

Answer 6

drive element (guide RNA, Cas9 and edited gene) on one of the chromosomes in a homologous pair. expressed Cas9 and guide that cuts the other chromosome, repair mechanism. both homologous chromosomes have drive element. induced homozygosity

Question 7

implementing drive element into germline

Answer 7

sperm cell with engineered drive element fused with egg cell to form zygote. drive element enters germline of developing offspring in the homozygous state so there is a 100% chance of it being passed on to the subsequent generation

Question 8

gene editing in mosquitos

Answer 8

edit mosquito gene which inhibits ability to transmit parasite next to genes encoding cas 9 and guide RNAs. release primary drive organism into wild population