Edexcel A Level Biology B
Edexcel A Level Biology B Topic 7: Modern Genetics Exam Questions
Free Edexcel A Level Biology B exam questions for Topic 7: Modern Genetics, with a mark scheme for every pack. Covers DNA sequencing, transcription factors, epigenetics, stem cells, recombinant DNA, PCR, gel electrophoresis and uses of gene technology.
Topic 7: Modern Genetics exam questions
4 question packs of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About Edexcel A Level Biology B Topic 7: Modern Genetics
Topic 7 of Edexcel A Level Biology B covers how modern techniques are used to study and change DNA. You learn how genomes are sequenced and how sequence data is used. The control of gene expression includes transcription factors and epigenetic modifications such as DNA methylation and histone acetylation, which can switch genes on or off without changing the base sequence. You study totipotent and pluripotent stem cells, including induced pluripotent stem cells, and their potential medical uses. Gene technology covers restriction enzymes, ligase, vectors, PCR and gel electrophoresis, and applications such as genetically modified organisms and gene therapy, along with their ethical issues.
What you need to know
- Gene sequencing DNA sequencing determines the order of bases. Automated high-throughput methods allow whole genomes to be sequenced and compared.
- Transcription factors Transcription factors bind to promoter regions and either stimulate or prevent RNA polymerase binding, controlling which genes are transcribed.
- Epigenetics DNA methylation usually silences genes; histone acetylation loosens chromatin and allows transcription. These changes can be influenced by the environment and some can be inherited.
- Stem cells Totipotent cells can form any cell type including placental cells; pluripotent cells can form most cell types. Induced pluripotent stem cells are made by reprogramming adult cells.
- Recombinant DNA Restriction endonucleases cut DNA at specific sites, ligase joins fragments, and vectors such as plasmids or viruses carry genes into host cells.
- PCR and electrophoresis PCR amplifies DNA through cycles of denaturation, annealing of primers and extension by Taq polymerase. Gel electrophoresis separates DNA fragments by size.
Common mistakes in Topic 7: Modern Genetics
- Saying epigenetic changes alter the DNA base sequence; they change gene expression without changing the sequence.
- Stating that methylation activates genes; DNA methylation usually silences them.
- Confusing totipotent with pluripotent stem cells.
- Writing that PCR copies RNA; PCR amplifies DNA.
- Forgetting that larger DNA fragments travel more slowly and so less far in gel electrophoresis.
Try three Topic 7: Modern Genetics exam-style questions
1. A PCR reaction starts with 20 DNA molecules. Calculate the number of molecules after 10 cycles. (2 marks)
Show the mark scheme answer
20 x 2^10; = 20 x 1024 = 20 480.
2. Explain how histone acetylation can increase transcription of a gene. (3 marks)
Show the mark scheme answer
Acetyl groups are added to histones; chromatin becomes less tightly packed; transcription factors and RNA polymerase can access the gene's promoter.
3. Describe how a gene can be inserted into a bacterial plasmid. (4 marks)
Show the mark scheme answer
Gene and plasmid cut with the same restriction enzyme; producing complementary sticky ends; gene and plasmid mixed so sticky ends pair; DNA ligase joins the sugar-phosphate backbone.
Topic 7: Modern Genetics FAQs
What does Edexcel A Level Biology B Topic 7: Modern Genetics cover?
It covers gene sequencing, transcription factors, epigenetics, stem cells, recombinant DNA technology, PCR, gel electrophoresis and applications of gene technology.
Which paper is Topic 7 examined in?
At A Level, this topic is assessed in Paper 1 and can also appear in Paper 3, which covers general and practical principles from all topics.
How should I answer questions on the ethics of gene technology?
Give balanced points with biological detail, such as medical or agricultural benefits against risks to ecosystems, unknown long-term effects and issues of consent and access.
