Homeschool Guide: These lesson plans are a guide for parents. Content may contain errors — always cross-reference with official exam board specifications.

dna and genetics

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4 detailed 50-minute lessons with teaching scripts, worked examples, parent guides, and assessment criteria.

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Lesson Overview

Total Lessons: 4
Tier: Foundation and Higher
Duration: 50 minutes per lesson (200 minutes total)
Exam Boards: AQA, Edexcel, OCR, Eduqas, CCEA

Learning Objectives

Prerequisites

Materials & Equipment

Lesson 1: Introduction: dna and genetics

Duration: 50 minutes

Starter Activity (5 minutes)

Quick Recall

Write down everything you already know about dna and genetics. Then check against the key terms: DNA and Genetics. Use a mini-whiteboard or paper.

Main Content (35 minutes)

Parent/Teacher Guide:
Before lesson: Read the script below. Pre-teach key vocab: DNA and Genetics.
If stuck: Re-read the revision notes (link above), then break the content into smaller steps.
Extension: See the Stretch & Challenge ideas in Lesson 4.
Teaching Script (35 mins):
Mins 0-5 - Hook: "Today: dna and genetics. By the end you will be able to answer exam questions on it unaided. It connects to the rest of Biology because the ideas here recur across the spec."
Mins 5-20 - Direct Instruction: Work through the core ideas below one at a time; after each, ask your student to explain it back in their own words.
Mins 20-30 - Guided Practice: Model the worked example together, then let your student attempt the first practice question with guidance.
Mins 30-35 - Independent Practice: 2-3 practice questions from Lesson 3 below, with immediate feedback.
First Look

Start with the revision notes summary, then attempt: Define the terms: gene, allele, genotype, phenotype, dominant, recessive.

Plenary (5 minutes)

Check Out

Your student states one thing they learned and one question they still have about dna and genetics.

Lesson 2: Core Concepts: dna and genetics

Duration: 50 minutes

Starter Activity (5 minutes)

Review Previous Lesson

Quick recap: write 3 key points from Lesson 1 on dna and genetics. Check them against the notes below.

Main Content (35 minutes)

DNA and Genetics: DNA carries the genetic code that determines an organism's characteristics. Understanding how genes and alleles are inherited allows us to predict the outcomes of genetic crosses using Punnett squares.
TermMeaningExample
Dominant alleleOnly one copy is needed for the characteristic to be expressed (shown). Represented by a capital letter (e.g. B).
Recessive alleleTwo copies are needed for the characteristic to be expressed. Represented by a lower case letter (e.g. b).
HomozygousBoth alleles are the same (e.g. BB or bb).
HeterozygousThe two alleles are different (e.g. Bb).
GenotypeThe combination of alleles an organism has for a gene (e.g. BB, Bb, or bb).
PhenotypeThe physical characteristic that is expressed (what you see, e.g. brown eyes or blue eyes).
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Practice (10 minutes)

Q: Define the terms: gene, allele, genotype, phenotype, dominant, recessive.

Answer: Gene: a short section of DNA that codes for a specific protein. Allele: different versions of the same gene. Genotype: the combination of alleles an organism has. Phenotype: the physical characteristic expressed. Dominant: allele that is expressed with only one copy. Recessive: allele that is only expressed with two copies.

Plenary (5 minutes)

Explain Back

Your student teaches the key points back to you without looking. Fill any gaps immediately.

Lesson 3: Application: dna and genetics

Duration: 50 minutes

Starter Activity (5 minutes)

Quick Recall

Recall the key terms: DNA and Genetics. Define each in one sentence.

Main Content (35 minutes)

Parent/Teacher Guide: Let your student attempt each question alone first, then compare with the model answer. Award method marks for correct working even if the final answer is wrong.

Q1: Define the terms: gene, allele, genotype, phenotype, dominant, recessive.

Answer: Gene: a short section of DNA that codes for a specific protein. Allele: different versions of the same gene. Genotype: the combination of alleles an organism has. Phenotype: the physical characteristic expressed. Dominant: allele that is expressed with only one copy. Recessive: allele that is only expressed with two copies.

Q2: In rabbits, black coat (B) is dominant over white coat (b). A heterozygous black rabbit is crossed with a white rabbit. Use a Punnett square to show the expected offspring ratios.

Answer: Bb × bb. Punnett square: Bb, Bb, bb, bb. Genotype ratio: 1 Bb : 1 bb. Phenotype ratio: 1 black : 1 white (50% each).

Q3: Explain the difference between homozygous and heterozygous. Give an example of each using the allele for cystic fibrosis.

Answer: Homozygous means both alleles are the same (e.g. FF = unaffected, ff = has cystic fibrosis). Heterozygous means the two alleles are different (e.g. Ff = carrier, unaffected but carries one recessive allele).

Q4: Polydactyly is caused by a dominant allele. Explain why two parents who both have polydactyly could have a child without polydactyly.

Answer: Both parents could be heterozygous (Dd). If Dd × Dd, there is a 1/4 (25%) chance of a child being dd (no polydactyly). The recessive allele d from each parent combines to give dd.

Q5: Both parents are carriers for cystic fibrosis (Ff). They already have one child with cystic fibrosis. What is the probability their next child will also have cystic fibrosis? Explain your answer.

Answer: The probability remains 1/4 = 25%. Each pregnancy is an independent event — the genotype of previous children does not affect the probability for the next child. Ff × Ff always gives 1/4 chance of ff.

Q6: Higher Explain how sex is determined in humans and why there is a 50% probability of each sex.

Answer: Sex is determined by the 23rd pair of chromosomes: XX = female, XY = male. The mother always contributes an X chromosome. The father contributes either X or Y. Punnett square: XX, XX, XY, XY. Therefore 50% chance of female (XX) and 50% chance of male (XY). The sperm determines the sex of the offspring.

Plenary (5 minutes)

Error Review

Review any questions answered incorrectly. Identify whether the error was knowledge, method, or reading the question.

Lesson 4: Exam Practice: dna and genetics

Duration: 50 minutes

Starter Activity (5 minutes)

Command Words

Review what these command words require: state (one point), describe (say what happens), explain (say why), compare (both sides), evaluate (judgement).

Main Content (35 minutes)

Extended Answer

Extended question: Extended Answer 6 marks: Explain genetic inheritance using a Punnett square. <div class="

Cystic fibrosis is caused by a recessive allele (f), so two copies are needed for the condition. When both parents are carriers (Ff), a Punnett square can predict the offspring genotypes. The father's gametes carry either F or f, and the mother's gametes carry either F or f. The Punnett square shows: FF (25%), Ff (50%), ff (25%). The genotype ratio is 1 FF : 2 Ff : 1 ff. Phenotypically, 75% of children will not have cystic fibrosis (FF + Ff), while 25% will have cystic fibrosis (ff). There is a 50% chance of each child being a carrier (Ff). Each pregnancy is an independent event, so the probability remains the same regardless of previous children. Carriers are unaffected because the dominant F allele produces enough functional protein. Mark scheme: 1 mark — correct parental genotypes identified; 1 mark — correct gametes shown; 1 mark — Punnett square drawn correctly; 1 mark — correct genotype ratio; 1 mark — correct phenotype ratio with percentages; 1 mark — explanation of carriers and independence of events.

Exam Tips: Always use the correct letter notation: capital for dominant, lower case for recessive (e.g. B and b) | When drawing Punnett squares, put one parent's alleles across the top and the other down the side | Always state BOTH the genotype ratio AND phenotype ratio in your answer | Remember: polydactyly is DOMINANT (only one allele needed), cystic fibrosis is RECESSIVE (two alleles needed) | Carriers have one recessive allele but do NOT show the characteristic (they are heterozygous) | You cannot be a carrier for a dominant disorder — if you have the allele, you have the condition | Each pregnancy is an INDEPENDENT event — previous children do not affect the probability for the next | Sex is dete
Common Errors: Watch Out! 1. Dominant alleles are more common. Wrong: dominant alleles are always the most frequent in a population. Correct: dominant refers to how an allele is expressed (only one copy needed), not how common it is — many recessive alleles are more common than dominant ones (e.g. the allele for polydactyly is dominant but rare). 2. Being a carrier means having the disease. Wrong: a carrier of a genetic disorder has the condition. Correct: a carrier has one recessive allele for the disorder but does not show symptoms because the dominant allele masks the recessive one; they are heterozygous and unaffected but can pass the allele to offspring.
AO3 - Reasoning & Interpretation: Analysis and Evaluation In a family, the parents are unaffected by cystic fibrosis but have a child with the condition. Draw a Punnett square to explain how this is possible. Their other two children are unaffected. What is the probability that each unaffected child is a carrier? If one of the unaffected children has a child with a partner who is also a carrier, what is the probability their child will have cystic fibrosis? Justify your answer using a second Punnett square.
Stretch & Challenge (Grade 8-9):
  • Synoptic links: explain how dna and genetics connects to another Biology topic you have studied
  • Real-world: research one real-world use or example of dna and genetics
  • Critical: "What are the limitations of the models used in dna and genetics?"

Plenary (5 minutes)

Assessment Criteria
  • Got it: Confident explanation + correct worked examples
  • Getting there: Main points OK, needs support with detail
  • Not yet: Confused on key concepts - re-run Lesson 2

Homework & Consolidation

Recommended Resources

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