Inheritance Foundations

Overview

Students build on prior learning about genes and chromosomes to develop the language needed to describe inherited variation. They then apply these terms to simple monohybrid Punnett squares, with the final exercise used as consolidation or a follow-up if time runs short.

Learning intentions

• WALT describe genes, alleles, genotypes and phenotypes.
• WALT distinguish dominant and recessive alleles.
• WALT distinguish homozygous and heterozygous genotypes.
• WALT use a Punnett square to predict possible offspring genotypes and phenotypes.

Success criteria

• I can define allele, genotype, phenotype, homozygous and heterozygous.
• I can explain how dominant and recessive alleles affect an observable characteristic.
• I can correctly complete and interpret a Punnett square.
• I can use scientific vocabulary to justify a prediction.

Curriculum links

• Genetic variation in relation to an identified characteristic: sources and nature of variation, and gene tracking.
• Science Learning Area Level 6: understanding how genetic information contributes to variation in characteristics.
• Nature of Science: communicating explanations using specific scientific language, symbols and conventions.
• Key Competencies: thinking; using language, symbols and texts; managing self; participating and contributing.

Lesson structure (60 minutes)

1. 0–8 min · Hook and recap. Open with the inheritance hook and recap slides and ask: “If two siblings have the same parents, why can their characteristics differ?” Clarify that a gene is a section of DNA carrying information for a characteristic, and that chromosomes occur in homologous pairs—one chromosome of each pair is inherited from each parent; homologous chromosomes carry the same kinds of genes but may carry different alleles. Students complete a quick think-pair-share and draw a simple homologous chromosome pair.

2. 8–17 min · Essential vocabulary. Use the key vocabulary slides to introduce each term with one consistent example, such as a simplified flower-colour characteristic. A genotype is the allele combination an individual has; a phenotype is the observable characteristic produced by the genotype and environmental influences. An allele is an alternative form of a gene. Students create a two-column glossary and answer: “Which term describes the DNA information, and which describes what we observe?”

3. 17–27 min · Dominance and allele combinations. Model the convention that a capital letter represents a dominant allele and a lower-case letter represents a recessive allele. Explain that a dominant allele is expressed in the phenotype when present, while a recessive allele is expressed only when no dominant allele is present; dominance does not mean “stronger” or more common. Define homozygous as two matching alleles, for example BB or bb, and heterozygous as two different alleles, for example Bb. Students classify BB, Bb and bb, then explain the phenotype expected for each using the glossary on the inheritance vocabulary and practice worksheet.

4. 27–40 min · Guided SCiPAD practice. Distribute the inheritance vocabulary and practice worksheet and direct students to the section corresponding to SCiPAD page 31. Students work independently for three minutes, compare answers with a partner, and then contribute answers for teacher checking. Pause to address the common errors “dominant means most common” and “heterozygous means two genes”. If the class has SCiPAD copies, students may complete page 31 in place of the worksheet section.

5. 40–50 min · Model a Punnett square. Return to the Punnett square modelling slides. Model a cross between two heterozygous parents, Bb × Bb: write one parent’s alleles across the top, the other parent’s alleles down the side, combine the alleles in each box, and count the possible genotypes and phenotypes. Emphasise that the square predicts probability, not the guaranteed characteristics of four actual offspring. Students copy the worked example, then complete two similar crosses in pairs and explain one answer to another pair.

6. 50–57 min · Independent application. Students attempt the Punnett square questions in the final section of the inheritance vocabulary and practice worksheet, or the selected questions from SCiPAD pages 32–33. Teacher conferences with students who confuse parent alleles with offspring genotypes. Students who finish early write a sentence explaining why two heterozygous parents can have a child with a recessive phenotype.

7. 57–60 min · Exit check and next step. Use the plenary and exit-question slide. Students submit three responses: define allele; classify Bb as homozygous or heterozygous and explain why; complete the first step of a Bb × bb Punnett square. Explain that unfinished SCiPAD page 32–33 work will begin the next lesson.

Resources

• the inheritance and Punnett square slide deck
• the inheritance vocabulary and practice worksheet
• SCiPAD Biology copies, pages 31–33
• Whiteboard and coloured pens
• Exercise books and pens
• Projector or interactive display
• Mini-whiteboards or scrap paper
• Exit-question display

Assessment

• Check students’ recap drawings and glossary definitions during questioning.
• Circulate during paired Punnett square work, checking correct placement of parental alleles and accurate genotype/phenotype language.
• Use the three-question exit check to identify students needing reteaching before the page 32–33 application.

Differentiation

• Provide a vocabulary bank, partially completed Punnett square and sentence starters such as “The genotype is … because …” and “The phenotype is … because …”.
• Use two colours to distinguish alleles from each parent and allow students to talk through each square before writing.
• Give EAL learners a visual glossary with the term, plain-English definition and example; read instructions aloud and check understanding privately.
• Extend confident students by asking them to calculate genotype and phenotype probabilities and explain why probability does not guarantee a particular outcome.