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Science lesson plan · 8th grade (Year 9 in England) · 45 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 · 5 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.
  1. What shape is a DNA molecule? (a single straight line / a ring of six atoms / a cube / a double helix) → a double helixPrompt: It looks like a twisted ladder.
  2. Human body cells have 23 pairs of chromosomes. How many chromosomes are in an egg cell? → 23Prompt: Is this a gamete (sex cell) or a body cell?
  3. Where is DNA found in an animal cell? (mainly in the nucleus / in the cell wall / outside the cell / in the chloroplasts) → mainly in the nucleusPrompt: It is the control centre of the cell.

Hook · 5 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 · 10 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 · 10 min

  • Do these together. Students try each step on whiteboards before you reveal it.
  • Use the hints as prompts rather than giving the answer.
  1. Which word means: the alleles an organism has, written like Bb? (allele / homozygous / genotype / dominant) → genotypePrompt: “Geno-” is about the genes you carry; “pheno-” is about what you see.
  2. The allele R (round seeds) is dominant over r. An organism has genotype rr. What is its phenotype? (shows round seeds / does not show round seeds) → does not show round seedsPrompt: One copy of a dominant allele is enough.

You do: independent practice · 10 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 8 questions are on the student sheet below, with answers in the key.

Exit ticket · 5 min

  • Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
  1. The allele F (free earlobes) is dominant over f. An organism has genotype ff. What is its phenotype? (shows free earlobes / does not show free earlobes) → does not show free earlobesPrompt: One copy of a dominant allele is enough.
  2. Which word means: having two identical alleles, such as BB or bb? (genotype / allele / heterozygous / homozygous) → homozygousPrompt: “Geno-” is about the genes you carry; “pheno-” is about what you see.

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

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Genes, alleles, genotypes and phenotypes

Name

Date

Score/ 8

  1. Question 1

    Which word means: having two different alleles, such as Bb?

    • A. allele
    • B. heterozygous
    • C. recessive
    • D. phenotype

  2. Question 2

    Genes and alleles: which statement is NOT true?

    • A. Most characteristics are controlled by several genes working together.
    • B. A recessive characteristic can skip a generation.
    • C. The phenotype can be affected by the environment as well as the genotype.
    • D. Dominant alleles are always the most common in a population.

  3. Question 3

    An organism has the genotype Rr. How is this genotype described?

    • A. homozygous dominant
    • B. heterozygous
    • C. homozygous recessive

  4. Question 4

    Which word means: having two identical alleles, such as BB or bb?

    • A. homozygous
    • B. heterozygous
    • C. phenotype
    • D. genotype

  5. Question 5

    An organism has the genotype Bb. How is this genotype described?

    • A. homozygous dominant
    • B. heterozygous
    • C. homozygous recessive

  6. Question 6

    An organism has the genotype Gg. How is this genotype described?

    • A. homozygous dominant
    • B. heterozygous
    • C. homozygous recessive

  7. Question 7

    Which word means: an allele that only shows its effect when two copies are present?

    • A. heterozygous
    • B. recessive
    • C. allele
    • D. phenotype

  8. Question 8

    An organism has the genotype FF. How is this genotype described?

    • A. homozygous dominant
    • B. heterozygous
    • C. homozygous recessive

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Answer key: Genes, alleles, genotypes and phenotypes

  1. 1. B. heterozygous

  2. 2. D. Dominant alleles are always the most common in a population.

  3. 3. B. heterozygous

  4. 4. A. homozygous

  5. 5. B. heterozygous

  6. 6. B. heterozygous

  7. 7. B. recessive

  8. 8. A. homozygous dominant