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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.
  1. What shape is a DNA molecule? (a double helix / a ring of six atoms / a single straight line / a cube) → 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. Human body cells have 23 pairs of chromosomes. How many chromosomes are in a sperm cell? → 23Prompt: 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.
  1. Which word means: an allele that only shows its effect when two copies are present? (dominant / heterozygous / recessive / phenotype) → recessivePrompt: “Geno-” is about the genes you carry; “pheno-” is about what you see.
  2. 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) → does not show brown furPrompt: One copy of a dominant allele is enough.

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.
  1. Genes and alleles: which statement is NOT true? (A recessive characteristic can skip a generation. / A heterozygous organism shows the recessive phenotype. / Most characteristics are controlled by several genes working together. / Body cells carry two alleles of each gene, one from each parent.) → A heterozygous organism shows the recessive phenotype.Prompt: Does “dominant” mean “most common”?
  2. The allele G (green pods) is dominant over g. An organism has genotype Gg. What is its phenotype? (shows green pods / does not show green pods) → shows green podsPrompt: 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

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Genes, alleles, genotypes and phenotypes

Name

Date

Score/ 6

  1. Question 1

    Which word means: a different version of a gene, such as B or b?

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

  2. Question 2

    Genes and alleles: which statement is NOT true?

    • A. Most characteristics are controlled by several genes working together.
    • B. A heterozygous organism shows the recessive phenotype.
    • C. Body cells carry two alleles of each gene, one from each parent.
    • D. The phenotype can be affected by the environment as well as the genotype.

  3. Question 3

    The allele F (free earlobes) is dominant over f. An organism has genotype Ff. What is its phenotype?

    • A. shows free earlobes
    • B. does not show free earlobes

  4. Question 4

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

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

  5. Question 5

    Which word means: the characteristic you can see, such as brown fur?

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

  6. Question 6

    The allele T (tall stems) is dominant over t. An organism has genotype TT. What is its phenotype?

    • A. shows tall stems
    • B. does not show tall stems

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Answer key: Genes, alleles, genotypes and phenotypes

  1. 1. C. allele

  2. 2. B. A heterozygous organism shows the recessive phenotype.

  3. 3. A. shows free earlobes

  4. 4. A. homozygous dominant

  5. 5. C. phenotype

  6. 6. A. shows tall stems