Mutations are caused by environmental factors known as mutagens. Examples of mutagens include radiation and certain chemicals. Germline mutations occur in gametes, and somatic mutations occur in other body cells. Mutations may alter entire chromosomes or change a single nucleotide. Their effects may be neutral, beneficial, or harmful. Mutations are essential for evolution because they are the ultimate source of genetic variation in a species.
- CA.9–12.IE.4.c; CA.9–12.LS.7.c
- NSES.9–12.C.2.3; NSES.9–12.C.3.1; NSES.9–12.F.1.1
- AAAS.9–12.5.A.1; AAAS.9–12.5.B.4, 5; AAAS.9–12.5.C.6; AAAS.9–12.5.F.3, 5; AAAS.9–12.6.E.2
- Identify causes of mutation.
- Compare and contrast types of mutations.
- Explain how mutations may affect the organisms in which they occur.
chromosomal alteration: mutation that changes chromosome structure
frameshift mutation: deletion or insertion of one or more nucleotides that changes the reading frame of the genetic material
genetic disorder: disease caused by a mutation in one or a few genes
germline mutation: mutation that occur in gametes
mutagen: environmental factor that causes mutations
mutation: change in the sequence of bases in DNA or RNA
point mutation: change in a single nucleotide base in the genetic material
somatic mutation: mutation that occurs in cells of the body other than gametes
Introducing the Lesson
Call on volunteers to describe drastic mutations they have read about or seen in science fiction stories or movies, or describe examples yourself. Explain that real mutations rarely have such drastic effects, but they are extremely important. Without them, evolution could not occur. Tell students they will learn more about mutations in this lesson.
Assign the activities at the URLs below. Students will investigate the effects of different mutations on the encoded proteins.
Pair less proficient readers with more proficient readers, and ask partners to make a table comparing and contrasting the following types of mutations: deletions, insertions, duplications, inversions, translocations, and point mutations. LPR
Ask a group of students to create a public service announcement identifying common mutagens that may cause cancer and ways that people can reduce their exposure to them. Have students make a video of their announcement and present it to the class or, if possible, the entire school.
Have students do the online activity Test Neurofibromin Activity in a Cell (see URL below). After reading about the protein neurofibromin and its role in normal cell division, students will predict how mutations in the gene for this protein might affect cell division. Then they will use an interactive animation to test their prediction. They will observe the simulated effects of different mutations on cells as though seen through a microscope.
Misconceptions about mutations are common. Discuss the examples below and give students the correct facts as well as examples of mutations that illustrate why the misconceptions are false.
1. All mutations are harmful.
Fact: Most mutations are neutral and some may even be beneficial. For several examples of beneficial mutations in yeast and bacteria, go to this link:
2. All mutations change the protein products of genes.
Fact: Some mutations have no effect on protein products. For example, mutations may occur in noncoding sections of DNA, or they may result in synonymous codons that code for the same amino acids.
3. All mutations have phenotypic effects.
Fact: Many mutations are recessive and do not affect phenotypes. Having one copy of the normal allele is sufficient for a normal phenotype. For example, the mutations that cause PKU and cystic fibrosis are recessive. Two copies of the recessive alleles must be present for the diseases to appear in the phenotype.
Reinforce and Review
Copy and distribute the lesson worksheets in the CK-12 Biology Workbook. Ask students to complete the worksheets alone or in pairs as a review of lesson content.
Have students answer the Review Questions listed at the end of the lesson in the FlexBook®.
Points to Consider
Sometimes even drastic mutations do not affect the proteins produced by a particular type of cell. The reason? The genes affected by the mutations are not normally used to make proteins in that type of cell. In all cells, some genes are turned off — they are not transcribed — while other genes are turned on.
- How do cells control which genes are turned on and used to make proteins?
- Can you think of a mechanism that might prevent transcription of a gene?