What this topic covers
Genetics, populations, evolution and ecosystems (A-level only) has 4 subtopics:
- Inheritance (A-level only)
- Populations (A-level only)
- Evolution may lead to speciation (A-level only)
- Populations in ecosystems (A-level only)
← Back to topics
A Level AQA Biology · Topic 7 of 8
Genetics, populations, evolution and ecosystems (A-level only) – A Level AQA Biology revision notes
Choose a subtopic. Genetics, populations, evolution and ecosystems (A-level only) covers Inheritance (A-level only), Populations (A-level only), Evolution may lead to speciation (A-level only), and Populations in ecosystems (A-level only) in A Level AQA Biology. 11 lessons in 4 subtopics.
Revise Genetics, populations, evolution and ecosystems (A-level only) for A Level AQA Biology, including Inheritance (A-level only).
11
Lessons
4
Subtopics
Genetics, populations, evolution and ecosystems (A-level only) lessons by subtopic
11 lessons, grouped by subtopic.
Inheritance (A-level only)
- Genotypes, Phenotypes, and Alleles: Define genotype and phenotype using precise AQA terminology, distinguishing between the two concepts; Explain how the environment interacts with genotype to produce phenotype, with biological examples; Compare dominant, recessive, and codominant alleles, justifying how each affects phenotype expression
- Monohybrid and Dihybrid Crosses: Construct fully labelled genetic diagrams for monohybrid crosses involving dominant, recessive, and codominant alleles; Construct fully labelled genetic diagrams for dihybrid crosses and predict phenotypic ratios; Interpret genetic cross results to determine parental genotypes and explain observed phenotypic ratios
- Advanced Inheritance Patterns: Explain the inheritance patterns produced by sex-linkage, autosomal linkage, multiple alleles, and epistasis, including the ratios expected from crosses; Construct and interpret genetic crosses involving two or more of these advanced inheritance patterns; Apply the chi-squared test to compare observed phenotypic ratios with expected ratios from a genetic cross
Populations (A-level only)
- Understanding Populations and Gene Pools: Define a population in precise biological terms, including the criteria of same species, shared space, shared time, and potential interbreeding; Explain how a species can exist as one or more geographically separated populations; Define gene pool and describe how it relates to the genetic diversity of a population
- The Hardy-Weinberg Principle: State the conditions required for the Hardy-Weinberg principle to apply to a population; Calculate allele, genotype, and phenotype frequencies using the Hardy-Weinberg equations $p + q = 1$ and $p^2 + 2pq + q^2 = 1$; Explain what a deviation from Hardy-Weinberg equilibrium suggests about a population
Evolution may lead to speciation (A-level only)
- Variation and Natural Selection: Explore the sources of variation within a population and how natural selection acts upon this variation.
- Genetic Drift and Speciation: Explain why genetic drift has a significant effect only in small populations; Explain how natural selection and reproductive isolation can change allele and phenotype frequencies, leading to the formation of a new species; Describe how reproductive separation leads to accumulation of differences in gene pools and eventual inability to interbreed
- Evolution and Biodiversity: Understand how evolution over long periods of time leads to a great diversity of species.
Populations in ecosystems (A-level only)
- Ecosystems, Niches and Population Dynamics: Define ecosystem, community, habitat, and niche using precise AQA terminology; Explain how abiotic and biotic factors govern the niche a species occupies; Describe how carrying capacity limits population size within an ecosystem
- Abiotic Factors, Interspecific Interactions and Quadrat Sampling: Explain how abiotic factors influence the distribution and abundance of organisms in a habitat; Compare interspecific and intraspecific competition, and describe the effects of predation on population size; Describe and evaluate the use of randomly placed quadrats and belt transects to sample populations
- Mark-Release-Recapture, Succession and Conservation: Calculate population size using the mark-release-recapture method and state the assumptions required; Describe the stages of primary succession from pioneer species to climax community; Explain how species modify abiotic conditions during succession, increasing suitability for subsequent species
Revise Right Mocks '26
AQA A-Level Biology mock draft, 26–31 Oct. Draft coverage: Biology 7402/1 · Paper 1. Reviewed for an original-practice sitting; check student availability before registering. Marking and results will follow later, after separate approval. Eligible new accounts receive a five-day Pro trial when signup email verification completes. Previous trials keep their original expiry. After expiry, new papers need Pro unless you have an explicitly confirmed free sitting offer for this event. That offer adds no Pro time or AI learning. Saved attempts and released results remain readable. No card or automatic charge.
More in this course
Go back to the full A Level AQA Biology topic list, or practise this topic with past-paper questions.
Frequently asked questions
What is Genetics, populations, evolution and ecosystems (A-level only)?
Genetics, populations, evolution and ecosystems (A-level only) covers Inheritance (A-level only), Populations (A-level only), Evolution may lead to speciation (A-level only), and Populations in ecosystems (A-level only) in A Level AQA Biology. 11 lessons in 4 subtopics.
What is an ecosystem?
An ecosystem is a community of organisms, the biotic component, together with the non-living abiotic components of the environment in which they live. The Ecosystems, Niches and Population Dynamics notes cover this in full.
What is an allele?
An allele is an alternative form of the same gene, differing in its nucleotide sequence, found at the same locus. The Genotypes, Phenotypes, and Alleles notes cover this in full.
What are the Hardy-Weinberg equations?
The Hardy-Weinberg equations are p + q = 1, where p and q are the frequencies of the dominant and recessive alleles, and p² + 2pq + q² = 1, where p² is the frequency of homozygous dominant individuals, 2pq of heterozygotes and q² of homozygous recessive individuals. The The Hardy-Weinberg Principle notes cover this in full.
What is a phenotype?
A phenotype is the observable characteristics of an organism, produced by the expression of its genotype in interaction with environmental factors. The Genotypes, Phenotypes, and Alleles notes cover this in full.
What is a niche?
A niche is the functional role a species plays in its ecosystem: what it eats, when it is active, what conditions it tolerates and what eats it. The Ecosystems, Niches and Population Dynamics notes cover this in full.
What is a genotype?
A genotype is the genetic constitution of an organism, the combination of alleles present at one or more loci. The Genotypes, Phenotypes, and Alleles notes cover this in full.
How do you calculate population size using mark-release-recapture?
Population size N = (n1 × n2) ÷ m2, where n1 is the number marked and released, n2 is the total caught in the second sample and m2 is the number of marked individuals in the second sample. The Mark-Release-Recapture, Succession and Conservation notes cover this in full.
What is coppicing?
Coppicing is a woodland management technique that creates a mosaic of light and shade at different stages of regrowth. The Mark-Release-Recapture, Succession and Conservation notes cover this in full.