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Step 3a: Mutations & Alleles

How did the disorder-causing allele arise?

What is Mutation?

This brief video introduces mutation at the DNA level as the source of variation in genes. The next two activities will explore the mechanism and result of mutation in further detail.

Project video to the whole class.

  • Mutation is a natural process that generates variation in DNA sequences

5 minutes

What is Mutation?

Mutate a DNA Sequence (online)

This activity offers a closer look at the types of DNA mutations that can happen and their consequences. Make a small change to a DNA sequence of a gene and see the effect on the resulting protein product.

Have students explore individually or in pairs.

  • The arrangement of DNA building blocks in a gene specifies the order of amino acids in the protein it codes for.
  • During DNA replication, occasional errors change DNA sequences. This process is called mutation.
  • Changing the order of DNA building blocks in a gene can change the order of amino acids in the protein that it codes for, thereby changing the structure and function of the protein.

15 - 20 minutes

Computers with internet access.

Mutate a DNA Sequence

Note:
To ensure your students understand frame shift mutations, you can review the content that's below the interactive.

Mutate a DNA Sequence (paper)

Using a paper model, students make a mutation of their choice (substitution, insertion, or deletion) in a gene during DNA replication. Then they transcribe and translate the mutated sequence to reveal the resulting amino acid sequence.

After completing the activity, students learn about the example gene and protein—Human Leukocyte Antigen (HLA-B)—including known variants.

Notes:

You may wish to review the following:

  • DNA replication follows base-paring rules: A-T, C-G
  • Sometimes during DNA replication, a base is inserted, deleted, or substituted with a different one, changing the DNA sequence of a gene.
  • Changes in the DNA sequence of a gene can lead to changes in the protein it codes for.
  • Only mutations in germ cells (eggs or sperm) can be passed to offspring.

As in reality, the mutations students make are random. There will be variation in the resulting amino acid sequence.

Students may be tempted to skip using the “molecular machinery” (ribosome) in this model. Encourage them to use it as a visual reminder of where proteins are assembled.

  • During DNA replication, occasional errors change DNA sequences. This process is called mutation.
  • Changes in DNA sequences can lead to changes in proteins.
Developing and/or Using Models

Using a paper model, students make a mutation and determine the effect on the resulting protein.

Cause & Effect

Students see the effect on a protein's structure caused by a change in a DNA sequence.

30-40 minutes

Scissors and tape

Student Instructions (pdf)

Make one copy per student or pair (copies may be re-used), or have students view on tables or computers:

Cut Outs (pdf)

Page 1 has two identical sets of strips. Give each student or pair a half-page:

Protein and Variant Information (pdf)

Make one copy per student or pair (copies may be re-used), or project to the class:

What is an Allele?

This short interactive uses blue vs. brown eye color to introduce alleles, showing how different versions of a gene lead to differences in protein function and traits.

  • Variations in DNA sequences of genes are called alleles.
  • Variations in DNA sequences lead to variations in proteins, which lead to variations in traits.

10 minutes