This free quiz has 11 real AQA A-level Biology exam questions on mutations and gene expression (28 marks, about 35 minutes). It marks itself: tick-box and calculation questions are marked for you, and for written answers you check your work against the real AQA mark scheme.
What the quiz covers (AQA 3.8.1–3.8.2)
how different types of gene mutation affect the polypeptide, including making it shorter
calculating the age of an embryo from a mutation rate
how transcription factors reprogramme cells to form iPS cells
how drugs with a similar structure to oestrogen treat ER-positive breast cancer
how methylation affects a gene, and how a drug that blocks methylation can reduce the effects of cancer
using RNA interference to explain the results of gel electrophoresis
how an altered KRAS gene can cause a tumour
how an inversion makes a non-functional protein, and evaluating iPS cells as a treatment for diabetes (4 marks each)
How to use it
Write each written answer in full before you open the mark scheme, then tick only the points you really made. Write about transcription, mRNA and translation rather than genes being “switched on” or “off”, and for the calculation show each step of your working.
Where students lose marks (from AQA examiners’ reports and mark schemes)
Each point below is followed by wording that gained marks.
Changed protein, not no protein. Many students said an altered gene meant no protein or a non-functional protein was made, which was rejected. Some wrote about uncontrollable cell growth rather than cell division.
✔ Gains credit: a mutation changes the amino acid sequence (primary structure) of the protein, or more of the protein is produced, resulting in rapid, uncontrollable cell division.
Transcribed, not “switched on”. Answers that said a gene was “switched on” or “switched off” weren't credited, and some students wrote “translated” when they meant transcribed.
✔ Gains credit: the gene is transcribed (mRNA is produced) or expressed, or its transcription is reduced or prevented.
Methylation of DNA, acetylation of histones. Marks were often lost by not saying it was the DNA or gene that is methylated, or by leaving out whether methylation increases or decreases. Acetylation of DNA was rejected and methylation of histones ignored.
✔ Gains credit: increased methylation of DNA inhibits transcription, while increased acetylation of histones stimulates transcription.
Epigenetics is not mutation. A surprising number of students suggested that epigenetic changes cause mutations, and any link between methylation and mutation was rejected. Far fewer referred to oncogenes than to tumour suppressor genes.
✔ Gains credit: decreased methylation of tumour suppressor genes allows their transcription, while increased methylation of oncogenes inhibits their transcription.
Promoters and RNA polymerase. Some students wrote DNA polymerase rather than RNA polymerase, or called the receptor's binding site an “active site”. Only the best answers mentioned the promoter or RNA polymerase at all.
✔ Gains credit: a transcription factor binds to the promoter region of DNA and stimulates RNA polymerase, so the gene is transcribed.
RNA interference acts on mRNA. Many students thought siRNA or antisense RNA binds to the gene or DNA and prevents transcription, and “translation of the gene” was called a fundamental mistake. Answers saying siRNA binds to the gene were rejected.
✔ Gains credit: the RNA is complementary to the mRNA, binds to it (or leads to its destruction) and so prevents translation.
Stem cells divide. Students often knew that stem cells renew themselves and differentiate, but didn't say that they divide or replicate. “Differentiate” is not the same as divide, and “grow” was ignored.
✔ Gains credit: transplanted stem cells divide (replicate) and differentiate into specialised cells, such as healthy blood cells.
Keep practising
The other AQA 3.8 self-marking quiz: Gene technologies
Topic 3.7 quizzes start with inheritance
The AQA topic index
weekly AQA group classes: Year 12 on Tuesdays at 5.15pm, Year 13 on Wednesdays or Thursdays at 6.30pm
Questions © AQA, from past A-level and AS Biology papers, with their mark schemes and examiners’ reports.