Written for this site from the class slides, with textbook page references for each statement. The chapter is on pages 643–647 of the course textbook. Image credits are on slide 11.
A gene knockout makes a chosen gene inoperative, usually by deleting or disrupting part of it. Comparing the knockout organism with normal ones shows what the gene does: mice without p53 develop many tumours; mice without the leptin gene overeat and become obese. Libraries of knockout strains exist for model species such as mice. Results may not transfer exactly to humans, and other genes can compensate.
Scientists design a guide RNA whose bases match the target DNA. It binds the enzyme Cas9, which is led to the matching sequence and cuts both strands. When the cell repairs the cut, the gene can be disabled or new DNA inserted. A successful use: blood stem cells from people with sickle cell disease are edited so their red blood cells make foetal haemoglobin, which does not sickle; the treatment was approved in 2023.
Conserved sequences are identical or similar across a species or group; highly conserved sequences have stayed similar over long periods of evolution, like histone genes in peas and humans. Two hypotheses explain this: the product only works with that sequence, so selection removes changes; or those regions have a slower rate of mutation.
Select a video to play it here. Select it again to close it.
Print this guide and complete it as you work through the slides and videos. It asks for your own explanations, so close the notes while you try each section.
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A printable worksheet covering all three statements, from quick recall to data questions and a longer answer. It has 30 marks and takes about 30 minutes, or you can do one section at a time.
Your teacher has the mark scheme.
You will need: Paper strip DNA sequence, guide RNA card, scissors as Cas9, tape, replacement sequence
Safety: Take care with scissors.
Carry this out with your teacher's supervision and follow your school's lab rules.
Doudna and Charpentier developed CRISPR-Cas9 editing. In 2018 He Jiankui's announcement of edited babies drew worldwide condemnation.
Consider the roles of scientists, governments and the public in setting limits on technology.
Summarised in our own words. Use each code to find the exact wording in your textbook or the IB subject guide.
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