Population Genetics and Epigenetics | OCR A-Level Biology B (Advancing Biology) (H422)
Population Genetics and Epigenetics
- 59 questions
- 4 subtopics
- Biology content, examined on all three papers
- Component 01, Component 02 and Component 03
Population Genetics and Epigenetics is examined in all three written papers — the specification states that Components 01, 02 and 03 can each assess content from any of the five modules, so nothing is confined to one paper.
It covers natural selection, sickle cell and malaria, the Hardy-Weinberg principle, genetic drift, the founder effect and speciation and epigenetics and gene expression.
Sample questions from Population Genetics and Epigenetics
Answer each one closed book first, then open the answer.
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Natural selection, sickle cell and malaria
Describe the phenotype of a person with the genotype Hbˢ Hbˢ.
Show the answer
They have sickle cell anaemia, with severe haemolytic anaemia and painful crises caused by sickled cells blocking vessels, and without medical treatment their survival is greatly reduced. -
Natural selection, sickle cell and malaria
Sickle cell anaemia results from a change to one amino acid. Explain why such a small change alters the protein so much.
Show the answer
Glutamic acid is polar and negatively charged while valine is non-polar, so replacing one with the other creates a hydrophobic patch on the surface of the β-globin chain and changes the way the molecules interact. -
The Hardy-Weinberg principle
State the conditions that must hold for the Hardy-Weinberg equations to apply.
Show the answer
The population must be large, mating must be random, and there must be no mutation, no migration into or out of the population and no natural selection acting on the gene. -
The Hardy-Weinberg principle
Where malaria is endemic, 1% of babies are born with sickle cell anaemia. Calculate the percentage of that population with sickle cell trait.
Show the answer
q² = 0.01 so q = 0.1 and p = 0.9, giving 2pq = 2 × 0.9 × 0.1 = 0.18, so 18% of the population has sickle cell trait. -
Genetic drift, the founder effect and speciation
Ellis-van Creveld syndrome is very rare worldwide but common in one Amish community in Pennsylvania. Explain why.
Show the answer
The community was founded by a very small group of settlers, at least one of whom carried the recessive allele, and it has grown in isolation with very little marriage outside it, so the allele frequency has remained far higher than in the general population. -
Genetic drift, the founder effect and speciation
Define the term species.
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A species is a group of organisms with similar characteristics that can interbreed to produce fertile offspring. -
Epigenetics and gene expression
How does histone acetylation increase gene expression?
Show the answer
Adding acetyl groups to the lysine residues of histone tails neutralises their positive charge, so they are less strongly attracted to the negatively charged phosphate groups of DNA; the chromatin becomes less condensed and the genes within it become accessible to transcription factors. -
Epigenetics and gene expression
What was found in people conceived during the Dutch Hunger Winter?
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Although of normal weight at birth, decades later they had higher rates of obesity, type 2 diabetes and cardiovascular disease, and they still showed reduced methylation of a growth-related gene some sixty years afterwards.
The 4 subtopics
One subtopic is one session. Work down the list.
| Subtopic | What it covers | Questions |
|---|---|---|
| Natural selection, sickle cell and malaria | Recall questions on natural selection, selection pressures and the gene pool, the phenotypes of Hbᴬ Hbᴬ, Hbᴬ Hbˢ and Hbˢ Hbˢ where malaria is endemic, heterozygote advantage, and how replacing glutamic acid with valine makes haemoglobin S polymerise and sickle cells. | 15 |
| The Hardy-Weinberg principle | Recall questions on what the principle assumes, what each term of the equation stands for, carrier frequency calculations for recessive conditions, and what a departure from the prediction means. | 14 |
| Genetic drift, the founder effect and speciation | Recall questions on genetic drift, the founder effect and genetic bottlenecks, Ellis-van Creveld syndrome in the Amish of Pennsylvania, ABO frequencies across populations, the risks of a reduced gene pool, and geographical and reproductive isolation in speciation, African primates and humans. | 15 |
| Epigenetics and gene expression | Recall questions on epigenetics, DNA methylation of promoters, histone acetylation and deacetylation, chromatin structure, environmental factors that alter the epigenome, the Norrbotten harvest records and the Dutch Hunger Winter, identical twin studies, type 2 diabetes, and epigenetic drugs. | 15 |
How the guide is worked
Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.
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Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
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Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
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Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.
Read the full method, the return schedule and the research behind it.
Nearby topics
OCR A-Level Biology B (Advancing Biology) Active Recall Guide
Every topic, not just this one. 2,895 questions with their answers.