Science lesson plan · 8th grade (Year 9 in England) · 30 minutes
Genes, alleles, genotypes and phenotypes
Cells, genetics and evolution
CCSS NGSS.MS-LS3-2England: KS3 Biology: Inheritance, chromosomes, DNA and genesEngland: GCSE Combined Science: Inheritance, variation and evolution
Objective and success criteria
Students will: Genes, alleles, genotypes and phenotypes.
- I can answer questions on today's skill on my own, without help.
- I can explain each step and say why it works.
- I can check my answer and spot a mistake.
Before and after
Needs first: DNA, genes and chromosomes
Leads to: Use twins and clones to separate genes from environment; Two-gene (dihybrid) crosses and 9 : 3 : 3 : 1 ratios
Materials: Microscope images or slides, Cell diagrams, Mini whiteboards, A diagram or short video clip of the idea, Printed student sheet (below).
Warm-up · 4 min
- Quick retrieval from earlier learning (DNA, genes and chromosomes). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- Where is DNA found in an animal cell? (in the cell wall / mainly in the nucleus / in the chloroplasts / outside the cell) → mainly in the nucleusPrompt: It is the control centre of the cell.
- Human body cells have 23 pairs of chromosomes. How many chromosomes are in a muscle cell? → 46Prompt: Is this a gamete (sex cell) or a body cell?
- Human body cells have 23 pairs of chromosomes. How many chromosomes are in a skin cell? → 46Prompt: Is this a gamete (sex cell) or a body cell?
Hook · 3 min
- Show a microscope image of cells and ask what students think they are looking at.
- Share the objective: Genes, alleles, genotypes and phenotypes. Read the success criteria together.
I do: model it · 7 min
- Work through the example out loud, saying why you do each step, not just what you do.
- Example: Which word means: a different version of a gene, such as B or b?
- Step 1: Alleles are different versions of the same gene.
- Step 2: So the answer is: allele
- Answer: allele
- Pause after each step and ask a student to say what comes next.
We do: guided practice · 6 min
- Do these together. Students try each step on whiteboards before you reveal it.
- Use the hints as prompts rather than giving the answer.
- Which word means: an allele that shows its effect with just one copy? (homozygous / dominant / genotype / phenotype) → dominantPrompt: “Geno-” is about the genes you carry; “pheno-” is about what you see.
- An organism has the genotype tt. How is this genotype described? (homozygous dominant / heterozygous / homozygous recessive) → homozygous recessivePrompt: Capital letters stand for dominant alleles.
You do: independent practice · 7 min
- Students work on the student sheet. Circulate and check the first two answers of every student early.
- Students who finish: write a question of their own for a partner, with the answer.
The 6 questions are on the student sheet below, with answers in the key.
Exit ticket · 3 min
- Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
- Genes and alleles: which statement is NOT true? (Dominant alleles are always the most common in a population. / Body cells carry two alleles of each gene, one from each parent. / A recessive characteristic can skip a generation. / The phenotype can be affected by the environment as well as the genotype.) → Dominant alleles are always the most common in a population.Prompt: Does “dominant” mean “most common”?
- The allele B (brown fur) is dominant over b. An organism has genotype BB. What is its phenotype? (shows brown fur / does not show brown fur) → shows brown furPrompt: One copy of a dominant allele is enough.
Watch out for
- Everyday meanings of words getting in the way of the science meaning: define key words explicitly.
- Remembering facts without the reason: ask "why?" and "what is the evidence?"
Support and stretch
Support
- Review first: DNA, genes and chromosomes.
- Use concrete materials: microscope images or slides.
- Give the first step of each question, or a partly worked example to finish.
- Pair with a confident partner for the guided practice.
Stretch
- Move on to: Use twins and clones to separate genes from environment; Two-gene (dihybrid) crosses and 9 : 3 : 3 : 1 ratios.
- Explain a common mistake in writing and how to fix it.
- Write a word problem that uses today's skill, then solve a partner's.
Homework and more practice
Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-8.
Free lesson plan from eurekami.com/lesson-plan-builder