Science // The Human Body

DNA & Genes

Describe the double helix structure of DNA (base pairs, complementarity), explain how genes are sections of DNA that code for proteins, introduce the central dogma (DNA → mRNA → protein) conceptually, and discuss the ethical implications of CRISPR gene editing — including potential benefits (genetic disease treatment) and concerns (germline editing, 'designer babies')

Ages
12 to 14
Type
Concept
Builds on
1 topic
Leads to
2 topics

Quick check

If the learner heard that scientists have edited a human gene to prevent a hereditary disease, could they explain what DNA actually is, how genes work, and why some people think editing human DNA raises serious ethical questions?

Ask this to see whether the topic is secure.

Topic // Mastery

What mastery looks like

What a learner can do once this topic is secure.
  • Describes DNA as a double helix with four bases (A, T, C, G) where A pairs with T and C pairs with G
  • Explains that a gene is a section of DNA that codes for a specific protein, and that proteins carry out most of the body's functions
  • Describes CRISPR as a molecular tool that can cut and edit DNA sequences, and raises at least two distinct ethical considerations about its use in humans

Topic // Map

Where this fits

What to learn first and what this topic opens up, with the reason for each link. Required links come first.
  • RequiredMust come first
  • HelpfulHelps, but not essential

Before this

1 topic
  • Chromosomes, Genes & DNARequired

    Ecosystems & Habitats // Ages 12 to 13

    DNA structure and replication depends on chromosomes and Mendelian inheritance

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DNA & Genes

Ages 12 to 14 // Concept

Leads to

2 topics
  • Cancer & Stem CellsRequired

    The Human Body // Ages 13 to 14

    Advanced gene expression and genetic disease mechanisms depends on DNA structure and replication

  • Predicting Inherited TraitsHelpful

    Ecosystems & Habitats // Ages 13 to 14

    DNA structure depends on Punnett squares and inheritance patterns

Topic // Research-informed

Teaching notes

From the Marble Skill Taxonomy. These notes have not been validated in classrooms, so treat them as a starting point for your own judgement.

The approach

Teach DNA and genes by building from structure to function to information. DNA is a double helix of complementary base pairs (A–T, C–G); a gene is a section of DNA whose base sequence codes for a protein; the central dogma (DNA → mRNA → protein) is a flow of INFORMATION, with proteins doing most of the body's work. Construct complementarity by hand rather than memorising it, make the base sequence tangibly behave as a code (a single base change alters one codon and can change the protein), and introduce CRISPR as a molecular tool that cuts and edits DNA. Handle the code/language analogy carefully to avoid seeding the well-documented error that translation synthesises amino acids. Teach CRISPR ethics as a socioscientific issue, grounding the science first before a genuinely two-sided discussion of somatic therapy versus germline editing.

Common misconceptions

  • The central-dogma arrows are misread — students do not interpret them as transfer of information.
  • Translation synthesises amino acids, rather than assembling pre-existing amino acids into a polypeptide (a persistent error since Fisher 1985).
  • The entire mRNA codes for protein — ignoring untranslated regions and non-coding sequence (start/stop codons, UTRs).
  • A gene conflated with its expression — believing a gene is present only when it is being expressed.
  • All mutations are harmful, and CRISPR can readily produce 'designer babies' — an over-simplified, sci-fi view of what editing does and how the code tolerates change.

Useful representations

  • Double-helix model whose antiparallel strands 'unzip' to expose complementary base pairs.
  • Base-pairing tiles (A↔T, C↔G) used to build the complementary strand.
  • Central-dogma information-flow diagram DNA → mRNA → protein with arrows labelled and information emphasised.
  • A codon→amino-acid decoding table used as a codebook.
  • A zoom from chromosome → gene → base sequence to locate a gene within the genome.

Teaching practices

  • Frame the central dogma explicitly as INFORMATION transfer and unpack what each arrow means (transcription, translation) — students routinely fail to read the canonical diagram as information flow.
  • Use the code/language analogy (bases → codons → amino-acid 'words' → protein) but correct the persistent 'translation makes amino acids' error — amino acids are pre-existing building blocks assembled into a polypeptide, not synthesised during translation.
  • Distinguish a gene (stored DNA information) from its expression (mRNA/protein made transiently) — students conflate the two and think genes exist only when expressed.
  • Build from the prerequisite (chromosomes–genes–DNA and Watson/Crick/Franklin) to complementarity through hands-on base-pairing modelling, so A–T / C–G is constructed rather than memorised.
  • Show that a single base change alters one codon and can change the protein — the concrete route into mutation and into what CRISPR edits.
  • Teach CRISPR ethics as a socioscientific issue: establish the science first, then structured discussion of somatic therapy vs germline editing, requiring at least two distinct considerations on each side without asserting a single right answer.

Activities to try

  1. 1

    Build the complementary strand by base-pairing

    Why it works: Base pairing is complementary and specific (A–T, C–G), not arbitrary; this specificity is what lets the sequence on one strand determine the other and lets DNA be copied faithfully.

    1. Start with a chromosome made from a long DNA molecule; zoom into a section of that molecule and mark a protein-coding gene. Then examine a DNA strand as a sequence of bases A,T,C,G.
    2. Build the partner strand by placing a complementary base against each base on the template: A opposite T, C opposite G, and only these pairings.
    3. Using paper tiles, printed cards, or an on-screen model where a correct base snaps into place and a mispair refuses to join, test what happens if you try to pair A with C or G.
    4. State in your own words why DNA can be copied faithfully if every base has exactly one partner.
    5. Optionally frame the discovery of the structure through the Watson/Crick/Franklin history, or an in-role interview with Rosalind Franklin, whose X-ray work helped reveal the helix — an optional companion for the structure, not a requirement.
  2. 2

    Decode a gene into a protein, then change one base

    Why it works: The base sequence is a code that carries information: a gene is read in three-base codons that specify which pre-existing amino acids are joined in order, and a single base change can alter the resulting protein. This is the concrete route into mutation and into what CRISPR edits.

    1. Use a supplied protein-coding DNA coding-strand segment and its corresponding mRNA sequence, both written in the reading direction. Compare them: the mRNA usesU wherever this coding-strand segment usesT. Read the mRNA in groups of three bases.
    2. Use an mRNA codon-to-amino-acid table to look up which amino acid each mRNA codon specifies; do not look up DNA triplets containingT in an RNA codebook.
    3. Assemble the amino acids in order into a polypeptide chain — selecting and ordering pre-existing amino-acid pieces (beads, cards, or draggable tiles), NOT creating new ones.
    4. Swap one base for a different base (a substitution) in the supplied coding-strand segment, update its corresponding mRNA base, and read the affected mRNA codon again with the codebook.
    5. Describe what happened to the protein: usually one amino-acid 'word' changes, sometimes the amino acid is unchanged (several codons can specify the same amino acid), and sometimes a codon becomes a 'stop' — all from a one-letter change in the code.
  3. 3

    Read the central dogma as information flow

    Why it works: The central-dogma arrows represent transfer of information from DNA to mRNA to protein; the gene is stored information that persists whether or not it is currently being expressed.

    1. Lay out the diagram DNA → mRNA → protein and label each arrow with the process it names (transcription for DNA → mRNA, translation for mRNA → protein).
    2. In your own words, say what is being passed along at each arrow — explain that the arrows show a flow of INFORMATION, not a physical object turning into another object.
    3. Order the steps of the central dogma yourself and explain where the gene's information ends up.
    4. Distinguish the gene (the stored DNA information, always present in the cell) from its expression (the mRNA and protein made transiently): a gene does not exist only when it is being expressed.

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