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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 is a gene? (a whole chromosome / a type of cell / a disease / a section of DNA that codes for a protein) → a section of DNA that codes for a proteinPrompt: Genes are found along chromosomes.
  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. What shape is a DNA molecule? (a single straight line / a double helix / a cube / a ring of six atoms) → a double helixPrompt: It looks like a twisted ladder.

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: having two identical alleles, such as BB or bb? (allele / genotype / dominant / homozygous) → homozygousPrompt: “Geno-” is about the genes you carry; “pheno-” is about what you see.
  2. An organism has the genotype FF. How is this genotype described? (homozygous dominant / heterozygous / homozygous recessive) → homozygous dominantPrompt: Capital letters stand for dominant alleles.

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. 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.
  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) → 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

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Genes, alleles, genotypes and phenotypes

Name

Date

Score/ 8

  1. Question 1

    Which word means: the alleles an organism has, written like Bb?

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

  2. Question 2

    Genes and alleles: which statement is NOT true?

    • A. A heterozygous organism shows the recessive phenotype.
    • B. Body cells carry two alleles of each gene, one from each parent.
    • C. Most characteristics are controlled by several genes working together.
    • D. A recessive characteristic can skip a generation.

  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

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

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

  5. Question 5

    The allele R (round seeds) is dominant over r. An organism has genotype rr. What is its phenotype?

    • A. shows round seeds
    • B. does not show round seeds

  6. Question 6

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

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

  7. Question 7

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

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

  8. Question 8

    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. D. genotype

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

  3. 3. A. shows free earlobes

  4. 4. A. homozygous

  5. 5. B. does not show round seeds

  6. 6. A. heterozygous

  7. 7. D. recessive

  8. 8. B. does not show tall stems