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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. How many chromosomes are in a normal human body cell? (12 / 46 (23 pairs) / 92 / 23) → 46 (23 pairs)Prompt: They come in pairs, one of each pair from each parent.
  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 is a gene? (a type of cell / a disease / a section of DNA that codes for a protein / a whole chromosome) → a section of DNA that codes for a proteinPrompt: Genes are found along chromosomes.

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? (phenotype / allele / dominant / homozygous) → homozygousPrompt: “Geno-” is about the genes you carry; “pheno-” is about what you see.
  2. An organism has the genotype Gg. How is this genotype described? (homozygous dominant / heterozygous / homozygous recessive) → heterozygousPrompt: 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. An organism has the genotype RR. How is this genotype described? (homozygous dominant / heterozygous / homozygous recessive) → homozygous dominantPrompt: Capital letters stand for dominant alleles.
  2. Which word means: the alleles an organism has, written like Bb? (recessive / heterozygous / phenotype / genotype) → genotypePrompt: “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: an allele that shows its effect with just one copy?

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

  2. Question 2

    Genes and alleles: which statement is NOT true?

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

  3. Question 3

    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

  4. Question 4

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

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

  5. Question 5

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

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

  6. Question 6

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

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

  7. Question 7

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

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

  8. Question 8

    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

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Answer key: Genes, alleles, genotypes and phenotypes

  1. 1. C. dominant

  2. 2. A. Every characteristic is controlled by one single gene.

  3. 3. A. shows round seeds

  4. 4. D. homozygous

  5. 5. A. homozygous dominant

  6. 6. B. heterozygous

  7. 7. B. phenotype

  8. 8. A. shows round seeds