IB Biology: Genetic Engineering & Biotechnology FAQs

It's the study of manipulating DNA for practical use — PCR, gel electrophoresis, recombinant plasmids and gene-editing tools like CRISPR-Cas9. According to the IB Biology guide (first assessments 2025), this content sits in Theme D 'Continuity and change', topic D3 (mutation and gene editing), and is tested across Paper 1, Paper 2 and Paper 3.

SL students need the core techniques — PCR, gel electrophoresis, recombinant DNA — and a working sense of CRISPR-Cas9's purpose. HL students go further: mechanism detail, more gene-technology case studies, and questions that expect you to evaluate applications like gene therapy, not just describe them.

You need to be able to explain, in sequence, how PCR amplifies DNA, how gel electrophoresis separates fragments by size and charge, how recombinant plasmids are built using restriction enzymes and ligase, and the basic principle behind CRISPR-Cas9 gene editing.

It's not conceptually difficult, but it's mark-heavy on precision. Students lose marks not from misunderstanding the science but from vague answers — saying 'DNA moves through the gel' instead of naming the mechanism (charge and fragment size) that examiners actually want stated explicitly.

The IB doesn't publish a fixed percentage per sub-topic, so there's no single number to memorise. But genetics and biotechnology content within Theme D is tested across all three papers, and Paper 3 data-based questions on gel electrophoresis or PCR results appear most exam sessions.

Top answers name the exact mechanism, not just the outcome. Instead of 'the gene is inserted', write 'restriction enzymes cut the plasmid and gene at complementary sticky ends, and DNA ligase seals the phosphodiester bonds.' Examiners reward that named-step precision far more than general description.

The most common one: confusing fragment size with distance travelled the wrong way round. Smaller fragments travel further, not less far — students consistently flip this under exam pressure. The second common slip is forgetting DNA is negatively charged and moves toward the anode, not the cathode.

Live gene-editing experiments aren't realistic for a school lab, but the topic still works well for an IA — bioinformatics-based investigations using published gel or PCR datasets, or a modelling exercise on restriction enzyme cut sites, both satisfy the exploration criterion without needing a wet lab.

Plot the known marker fragment sizes against migration distance on semi-log graph paper — the relationship is roughly linear on a log scale. Measure your unknown band's distance, read across to the line of best fit, then convert back from the log axis to get its size in base pairs.

IB questions regularly ask you to evaluate, not just describe, applications like GM crops, gene therapy, and human gene editing. Expect to weigh benefits (disease resistance, yield, treating genetic disorders) against risks (unknown ecological effects, consent issues, unequal access) using specific named examples, not generic opinion.

It's a different kind of demand rather than simply harder. Biology's genetic engineering topic asks for precise mechanistic explanation and data interpretation; Chemistry's related organic and biochemistry content is more calculation-heavy; ESS covers biotechnology's environmental and social angle with less molecular mechanism detail.

Look for resources that pair concise topic notes with past-paper-style practice questions and full mark schemes — this topic is won and lost on how precisely a student writes an answer, not on general understanding, so worked feedback matters more than another textbook summary.