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Module 6: Genetics, evolution and ecosystems
Quick questions on Manipulating genomes: DNA sequencing, PCR, electrophoresis, genetic engineering and DNA profiling - OCR A-Level Biology A
7short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is dNA sequencing?Show answer
DNA sequencing determines the order of bases in a length of DNA. Modern high-throughput (next-generation) methods sequence whole genomes rapidly and cheaply, allowing comparison of genomes between species (for phylogeny) and between individuals (for medicine). Knowing the sequence lets us predict the amino acid sequence and so the protein.
What is gel electrophoresis?Show answer
Gel electrophoresis separates DNA fragments by size. DNA samples are placed in wells in an agarose gel and an electric field is applied; because DNA is negatively charged (its phosphate groups), the fragments move towards the positive electrode. Smaller fragments move faster and further through the gel mesh, so the fragments separate into bands by length. It is used in sequencing and DNA profiling.
What is gene editing?Show answer
Gene editing (for example using CRISPR-Cas9) allows precise changes to a specific DNA sequence: a guide molecule targets the enzyme to an exact site, where it cuts the DNA so a base sequence can be removed, corrected or added. It is far more precise than older methods and has potential to correct disease-causing mutations.
What is dNA profiling?Show answer
DNA profiling identifies individuals from the variable, non-coding regions of their DNA (short tandem repeats, which vary in number between people). The steps are: extract the DNA, amplify the repeat regions by PCR, cut or separate them, and run gel electrophoresis to produce a pattern of bands (the profile). The chance of two unrelated people sharing a profile is tiny, so it is used in forensics, paternity testing and studying relationships.
What is q1?Show answer
State the three temperature stages of PCR and what happens at each. [3 marks]
What is q2?Show answer
Explain why smaller DNA fragments travel further in gel electrophoresis. [2 marks]
What is q3?Show answer
Name the enzyme used to join the sugar-phosphate backbones when making recombinant DNA. [1 mark]
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