Genetic Engineering and Genomics
What the exam tests
Genetic engineering and genomics questions ask you to order the steps of recombinant DNA technology, choose tools correctly, and explain applications such as PCR, DNA fingerprinting, and gene therapy. Genomics includes the Human Genome Project and comparative genomics.
Core rules
- Restriction endonucleases cut DNA at palindromic recognition sites, often producing sticky ends; DNA ligase joins compatible ends.
- A cloning vector needs an origin of replication, a selectable marker, and a recognition site for insertion; plasmids and bacteriophages are common vectors.
- Transformation introduces recombinant DNA into a host; selection uses antibiotic resistance or screening (e.g., blue-white selection).
- PCR uses denaturation, primer annealing, and extension by Taq polymerase; product doubles each cycle.
- DNA fingerprinting uses variable number tandem repeats (VNTRs) and gel electrophoresis; it is used in forensics and paternity testing.
Worked example
A gene must be inserted into a plasmid cut with EcoRI. The gene is amplified by PCR using primers that add EcoRI sites at both ends. After digestion with EcoRI, the insert and plasmid have compatible sticky ends; ligase seals them. If PCR starts with one DNA molecule and runs 10 cycles, the number of copies is 2^10 = 1024. Reasoning: each cycle doubles the target sequence, so the increase is exponential, not linear.
Traps
Do not confuse restriction enzymes (cut) with ligase (join). Blunt-end ligation is less efficient than sticky-end ligation. A selectable marker keeps transformed cells alive; a reporter gene reveals expression. In PCR, primers must bind opposite strands and flank the target. In gel electrophoresis, smaller fragments move farther.