Population Genetics and Epigenetics

What Population Genetics and Epigenetics covers

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.

The 4 subtopics

Each one has its own page.

• Natural selection, sickle cell and malariaRecall 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.Open →
• The Hardy-Weinberg principleRecall 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.Open →
• Genetic drift, the founder effect and speciationRecall 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.Open →
• Epigenetics and gene expressionRecall 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.Open →

What you need to know

Answer each one before you reveal it.

Take Population Genetics and Epigenetics further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

• Founder effect vs Genetic bottleneck

  Founder effect: a new population is started by a small number of individuals leaving the original one, carrying an unrepresentative sample of its alleles. Genetic bottleneck: an existing population is drastically reduced by a famine, an epidemic or a disaster, so the survivors carry only a fraction of the alleles it had.

• Genetic drift vs Natural selection

  Genetic drift: a change in allele frequencies that happens purely by chance from one generation to the next, with the largest effect in small populations. Natural selection: a change in allele frequencies in which better-adapted individuals survive and breed more, so advantageous alleles increase predictably.

• The term p² vs The term 2pq

  The term p²: the proportion of a population that is homozygous for the dominant allele. The term 2pq: the proportion of a population that is heterozygous, doubled because that combination can be formed in two ways depending on which parent supplies which allele.

Questions from this topic

Each one with the model answer underneath.

1. 1

   How does natural selection change allele frequencies within a population?

   Model answer

   Individuals whose alleles give an advantage in the current environment survive and reproduce more successfully, so they pass those alleles to more offspring and the frequency of the advantageous allele rises over the generations.

2. 2

   What is meant by a selection pressure?

   Model answer

   A selection pressure is an environmental factor, such as a disease, a predator or a shortage of food, that makes the survival and reproduction of some phenotypes more likely than others.

3. 3

   Define the term gene pool.

   Model answer

   The gene pool is all the alleles of all the genes present in all the individuals of a population at a given time.

4. 4

   Describe the phenotype of a person with the genotype Hbᴬ Hbᴬ living where malaria is endemic.

   Model answer

   They make only normal haemoglobin and have no anaemia, but they have no protection against the malarial parasite and are at high risk of severe, potentially fatal malaria.

5. 5

   Describe the phenotype of a person with the genotype Hbᴬ Hbˢ.

   Model answer

   They have sickle cell trait: about half of their haemoglobin is haemoglobin S, so they are essentially healthy and sickle only under extreme oxygen shortage, and they are substantially protected against severe malaria.

6. 6

   Describe the phenotype of a person with the genotype Hbˢ Hbˢ.

   Model 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.

What is inside Levo

Six ways to work the same material.

Population Genetics and Epigenetics revision questions

What does Population Genetics and Epigenetics cover in OCR A-Level Biology B?

4 subtopics: natural selection, sickle cell and malaria, the hardy-weinberg principle, genetic drift, the founder effect and speciation and epigenetics and gene expression. Each one has its own page with questions and model answers.

How is Population Genetics and Epigenetics organised?

By the OCR H422 specification, subtopic by subtopic, so it matches the order you are taught it in.