It is expressed in the phenotype when at least one copy is present (in a heterozygote). Learn it step by step →
Inheritance, Variation & Evolution is a core part of GCSE Biology. Revise the key concepts and common mistakes below, then lock them in with the free games.
Key concepts
GeneShort section of DNA coding for a particular protein
AlleleDifferent version of the same gene (e.g. B or b)
GenotypeThe combination of alleles an organism carries
PhenotypeObservable characteristic produced by the genotype
HomozygousTwo identical alleles for a gene (BB or bb)
HeterozygousTwo different alleles for a gene (Bb)
Punnett squareGrid used to predict offspring genotypes from a cross
Monohybrid crossCross involving one gene with two alleles
Dominant alleleAllele expressed even when only one copy is present
Recessive alleleOnly expressed when both alleles are recessive
ProbabilityChance of an outcome — as fraction, ratio or %
CarrierHeterozygote carrying but not showing a recessive trait
SpeciationFormation of two new species from one ancestor
Selective breedingChoosing parents with desired traits to breed
What your exam board covers
Where Inheritance, Variation & Evolution sits in each exam board's specification. Tap a board to see what it lists.
AQAInheritance, variation and evolutionSpec 8461
Reproduction
Variation and evolution
The development of understanding of genetics and evolution
Questions where students often pick the tempting wrong answer — make sure you know the right one:
What does it mean for an allele to be 'dominant'?✗ A dominant allele is the most common allele in a population.✓ It is expressed in the phenotype when at least one copy is present (in a heterozygote).
What does a gene code for?✗ A gene codes for a specific physical feature like eye colour directly.✓ Typically a polypeptide (protein) — through transcription to mRNA and translation by ribosomes.
How does a population of organisms become better adapted to its environment over time?✗ Individual organisms change during their lifetime in response to their environment and pass the changes on to offspring.✓ Individuals with advantageous heritable variations survive and reproduce more; their alleles increase in frequency over generations.
Is a mutation always harmful to an organism?✗ Every mutation is harmful and damages the organism.✓ No — most mutations are neutral (no effect), some are harmful, and a few are beneficial.
Where in a cell is DNA mostly found?✗ In the cytoplasm✓ In the nucleus
Practise Inheritance, Variation & Evolution — free games
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