Key term
OCR GCSE Biology A J247
Cell Level Systems
Topic overviewMicroscopy, and sub-cellular structuresDNA structure: polymer, double helix and nucleotidesProtein synthesis and the triplet codeEnzyme action, and investigating enzymesCellular respiration as an exothermic processAerobic and anaerobic respiration comparedSynthesis and breakdown of carbohydrates, proteins and lipidsPhotosynthesis: producers and the processPhotosynthesis as endothermic, and investigating itLimiting factors in photosynthesis
Community Level Systems
Genes, Inheritance and Selection
Topic overviewGenetic terms, and the genomeGenome, environment and mutationsHow genetic variants influence phenotypeAsexual and sexual reproduction comparedHaploid, diploid and meiosisSingle gene inheritance and Punnett squaresSex determination, multiple genes and Mendel's workVariation within a population, and classificationNatural selection and evolutionEvidence for evolution, and the work of Darwin and Wallace
Global Challenges
Topic overviewField investigations, and human impact on ecosystemsMaintaining biodiversity, and evidence for environmental changeFood security, agricultural and biotechnological solutionsSelective breeding and genetic engineeringHealth, disease, and types of diseaseInteractions between diseases, and how they spreadReducing the spread of disease, and named examplesPhysical and chemical plant defencesDetecting plant disease; white blood cells and plateletsNon-specific defences and the immune systemMonoclonal antibodies and their usesVaccines, medicines and aseptic techniqueDeveloping new medicines, and non-communicable diseaseTreating cardiovascular disease, and lifestyle factorsCancer, and the use of stem cells in medicineGene technology in medicine, and the human genome
Organism Level Systems
Topic overviewThe nervous system and coordinated responsesThe reflex arcThe eye and its common defectsThe structure and function of the brainInvestigating and treating the brainHormonal coordination, thyroxine and adrenalineHormones in reproduction and the menstrual cycleContraception and treating infertilityPlant hormones and their commercial usesHomeostasis, and the skin in temperature controlInsulin and glucagon in blood sugar controlType 1 and type 2 diabetesOsmotic changes in body fluids, and the kidneysThe kidney tubule and the effect of ADHResponding to temperature and osmotic challenges
Scaling Up
Topic overviewDiffusion, osmosis and active transportMitosis, the cell cycle and cell differentiationStem cells in animals and meristems in plantsSurface area to volume ratio and exchange surfacesThe circulatory system, the heart and blood vesselsRed blood cells and plasmaRoot hair cells, transpiration and translocationXylem and phloemFactors affecting water uptake, and the potometer
Genes, Inheritance and Selection
- 10 subtopics
- 30 things to know
- Paper 4
What Genes, Inheritance and Selection covers
Genes, Inheritance and Selection is examined in Biology A Paper 4. It covers genetic terms and the genome; genome, environment and mutations; how genetic variants influence phenotype; asexual and sexual reproduction compared; haploid, diploid and meiosis; single gene inheritance and Punnett squares; sex determination, multiple genes and Mendel's work; variation within a population and classification; natural selection and evolution; and evidence for evolution and the work of Darwin and Wallace.
Where it is assessed
Paper 4
Biology A Paper 4: 1 hour 45 minutes, 90 marks, 50% of the GCSE.
Check the OCR specification ↗The 10 subtopics
Each one has its own page.
- Genetic terms, and the genomeWhat gametes, chromosomes, genes and alleles are, dominant and recessive alleles, homozygous and heterozygous, genotype and phenotype, writing genotypes and working out a phenotype, what a genome is and that it includes non-coding DNA, how a gene and a genome differ, where the genome is found, why individuals' genomes differ, and what sequencing a genome means.Open →
- Genome, environment and mutationsHow the genome and the environment together determine phenotype, discontinuous and continuous variation with examples such as eye colour and height and how each is usually controlled, mutations as the source of all genetic variants, the three possible effects of a mutation on the phenotype and which is rarest, why most have no effect, and why not all mutations are harmful.Open →
- How genetic variants influence phenotypeThe two ways a variant can change the phenotype, how a change in coding DNA alters a protein or an enzyme, and how a variant in non-coding DNA changes how much protein is made.Open →
- Asexual and sexual reproduction comparedThe advantages and disadvantages of asexual and sexual reproduction, why an asexual population can be wiped out by a new disease, how offspring numbers compare between bacteria and large mammals, when asexual reproduction is an advantage, why many plants reproduce both ways, and why the variation from sexual reproduction helps a population survive a new predator.Open →
- Haploid, diploid and meiosisWhat haploid and diploid mean, human chromosome numbers in body cells and gametes, why a fertilised egg and an embryo's cells are diploid, how meiosis halves the chromosome number to make four gametes, how meiosis and fertilisation keep the number constant, meiosis as a source of variation, where it happens, and how it compares with mitosis.Open →
- Single gene inheritance and Punnett squaresWhat single gene inheritance is, predicting offspring genotypes and phenotypes from crosses of homozygous and heterozygous parents, what a carrier is and why a recessive characteristic needs two recessive alleles, a test cross to find an unknown genotype, using Punnett squares to give ratios, numbers and probabilities, and why each fertilisation is independent.Open →
- Sex determination, multiple genes and Mendel's workThe X and Y chromosomes and which parent decides a child's sex, the Punnett square for the cross, characteristics controlled by many genes, and Mendel's pea crosses and their late acceptance.Open →
- Variation within a population, and classificationHow much genetic variation a population holds and where it comes from, why individuals carry the same genes in different variants, why variation helps a population and sexual reproduction gives more of it, what classification is, artificial and natural classification with examples, molecular phylogenetics and how DNA sequencing reveals relationships, and why classification changes over time.Open →
- Natural selection and evolutionWhat natural selection is, where variation comes from, the steps from mutation to a changed population, why individuals do not evolve, what evolution and a species are, and how new species form.Open →
- Evidence for evolution, and the work of Darwin and WallaceFossils and antibiotic resistance as evidence for evolution, why the fossil record is incomplete, how bacteria become resistant, Darwin's and Wallace's theory and its slow acceptance, and what seedbanks preserve.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
Which chromosome pair determines sex in humans, what does each sex carry, and which parent decides a child's sex and why?
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A population is split in two by a mountain range. Explain how this can lead to two new species.
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What is a gamete?
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What is discontinuous variation?
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What are the two broad ways in which a genetic variant can influence the phenotype?
Evaluation
Give two advantages of asexual reproduction.
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What is meant by single gene inheritance?
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What produces the genetic variation found within a population?
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Give two lines of evidence for evolution.
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What is a chromosome?
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What is continuous variation?
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What is coding DNA?
Evaluation
What is the main disadvantage of asexual reproduction?
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What does haploid mean?
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A homozygous dominant parent is crossed with a homozygous recessive parent for the same gene. What genotype do all the offspring have?
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Which pair of chromosomes determines sex in humans?
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What does it mean to say there is extensive genetic variation within a population of a species?
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What is natural selection?
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What is a fossil?
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What is a gene?
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Give two human characteristics that show continuous variation.
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What is non-coding DNA?
Evaluation
Give two disadvantages of sexual reproduction.
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Which human cells are haploid?
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What is a carrier of a recessive allele?
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What sex chromosomes does a human female have, and what sex chromosomes does a human male have?
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What is an artificial classification system based on?
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Explain why natural selection cannot work without variation.
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Why is the fossil record incomplete?
Take Genes, Inheritance and Selection further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Genotype vs Phenotype
Genotype: combination of alleles an organism carries for a gene. Phenotype: observable characteristics of an organism.
Homozygous vs Heterozygous
Homozygous: carrying two identical alleles of a gene. Heterozygous: carrying two different alleles of a gene.
Haploid vs Diploid
Haploid: containing a single set of chromosomes, one copy of each. Diploid: containing two sets of chromosomes, one inherited from each parent.
Questions from this topic
Each one with the model answer underneath.
- 1
What is a gamete?
Model answer
A sex cell that carries a single set of chromosomes and fuses with another gamete at fertilisation.
- 2
What is a chromosome?
Model answer
A long coiled molecule of DNA, found in the nucleus, that carries many genes along its length.
- 3
What is a gene?
Model answer
A section of DNA that codes for a particular protein and so contributes to a characteristic.
- 4
What is an allele, also called a variant?
Model answer
A different version of the same gene, found at the same position on a chromosome.
- 5
What does it mean to say that an allele is dominant?
Model answer
Only one copy of it is needed for it to be shown in the phenotype.
- 6
What does it mean to say that an allele is recessive?
Model answer
Two copies of it are needed for it to be shown, because a dominant allele masks it whenever one is present.
What is inside Levo
Six ways to work the same material.
Genes, Inheritance and Selection revision questions
- What does Genes, Inheritance and Selection cover in OCR GCSE Biology A?
- 10 subtopics: genetic terms, and the genome, genome, environment and mutations, how genetic variants influence phenotype, asexual and sexual reproduction compared, haploid, diploid and meiosis, single gene inheritance and punnett squares, sex determination, multiple genes and mendel's work, variation within a population, and classification, natural selection and evolution and evidence for evolution, and the work of darwin and wallace. Each one has its own page with questions and model answers.
- How is Genes, Inheritance and Selection organised?
- By the OCR J247 specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Genes, Inheritance and Selection, on a schedule.
Attempt a question from memory, write the correct version, then attempt it again. Levo records the jump between your first attempt and your last, and brings each question back on the day you are due to forget it.
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