Question 1

What is the difference between reproductive and therapeutic cloning?

Accepted Answer

Reproductive cloning aims to produce a genetically identical organism, such as Dolly the sheep, using somatic cell nuclear transfer (SCNT). Therapeutic cloning also uses SCNT but to create embryos for harvesting stem cells, which can be used to treat diseases like Parkinson's or spinal cord injuries. The key difference is that therapeutic cloning does not result in a live birth; the embryo is destroyed to obtain stem cells, raising ethical concerns.

Question 2

How does PCR work step by step?

Accepted Answer

PCR (polymerase chain reaction) amplifies a specific DNA sequence in three steps: 1) Denaturation at 95°C – heat separates the double-stranded DNA into single strands. 2) Annealing at 50-65°C – primers bind to complementary sequences on each strand. 3) Extension at 72°C – Taq DNA polymerase adds nucleotides to the primers, synthesising new strands. These steps are repeated for 25-35 cycles, doubling the DNA each time.

Question 3

Why is Taq polymerase used in PCR instead of human DNA polymerase?

Accepted Answer

Taq polymerase is derived from the thermophilic bacterium Thermus aquaticus, which lives in hot springs. It is heat-stable and remains active at the high temperatures (95°C) used to denature DNA during PCR. Human DNA polymerase would denature and lose function at such temperatures, so Taq is essential for the repeated heating cycles.

Question 4

What are the ethical issues with cloning?

Accepted Answer

Ethical issues include the low success rate and high failure rate in animal cloning (e.g., Dolly was the only successful clone out of 277 attempts), leading to animal suffering. There are concerns about reducing genetic diversity, which makes populations vulnerable to disease. In human cloning, issues include the moral status of embryos, potential for exploitation, and the risk of psychological harm to clones. Many countries have banned reproductive human cloning.

Question 5

How do you select transformed bacteria in gene cloning?

Accepted Answer

After transformation, bacteria are grown on agar plates containing an antibiotic (e.g., ampicillin). The plasmid vector carries an antibiotic resistance gene, so only transformed bacteria (which have taken up the plasmid) survive. To distinguish bacteria with the recombinant plasmid (containing the target gene), a second marker gene (e.g., lacZ) is often used; if the target gene is inserted into lacZ, it disrupts the gene, and colonies appear white instead of blue on X-gal medium.

Question 6

What is the role of restriction enzymes in genetic engineering?

Accepted Answer

Restriction enzymes (restriction endonucleases) cut DNA at specific recognition sequences, usually palindromic, producing sticky or blunt ends. They are used to cut the target gene from the donor DNA and to cut the vector (e.g., plasmid) at the same site, creating complementary ends. This allows the target gene to be inserted into the vector using DNA ligase. Different restriction enzymes recognise different sequences, so choosing the right one is crucial for successful cloning.

Cloning and biotechnology

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