Mutations, part 1
Lesson 8 of 16
Objective: Students will be able to describe the relationships between changes in DNA and potential appearance of new traits including insertions, deletions and substitutions.
Warm-Up: What words and images come to mind when you hear the words mutation or mutant?
Before allowing students to share their thoughts, show a clip from the X-Men movie or Teenage Mutant Ninja Turtles.
Most students know about the X-Men or the Teenage Mutant Ninja Turtles so the movie clip will serve to “hook” students into the discussion that will follow.
Because many students are not able to separate fact from fiction, the clip also helps to initiate the discussion about what is a mutation and what is fantasy. After the clip, allow students to share their thoughts. Listen to see if misconceptions surface while students are sharing. Make sure that the discussion ends with students fully aware that mutations of the X-men type are not real.
However, explain that some mutations are so unusual that they may appear to be fictional. Show the video clip, Real Mutations in animals and humans (graphic) or a clip, Mermaid syndrome. Note: Watch the real mutations in animals and humans clip beforehand to decide if the video is appropriate for your student audience.
Explain that the students will examine some of the causes of mutations and learn the types of mutations that can occur.
Introduce New Material
Begin the lesson by introducing the vocabulary associated with the lesson: mutation, carcinogen, deletion, insertion, substitution, frameshift mutation, lethal, translocation, inversion, silent mutation
Say each word aloud and ask students to repeat the term after you. Clap out the syllables for the terms with 3 or more syllables. This helps students hear the word parts of more complex words so that they can pronounce them correctly.
Provide explicit instruction of each term when it arises during the course of instruction.
Inform students of the learning targets for this lesson:
- I can identify mutagenic factors that can alter DNA.
- I can distinguish between different types of mutations.
Display visual information as you instruct and ensure students take notes using Genetic Mutations guided notes that you provide or use a note-taking strategy that you have taught. Guided notes provide greater support for the different learning styles of students.
Spend time discussing each of the different types of mutations and show students examples of each type. For example, show students the two sentences below. Show what happens when a single letter in one of the words from the first sentence is changed:
– THE DOG BIT THE CAT.
– THE DOG BIT THE CAR.
This simple strategy shows how only one letter change has a great impact. This type of example using real words (but written as triplets) helps students understand how changing one letter changes the entire meaning of a DNA code.
from the full video, Cracking the Code. This clip is a gripping tale of two families (twin brothers) whose lives are tragically impacted by Tay-Sachs’ disease. Know that some students may be moved to tears while watching this clip. Be prepared to talk empathy and how its’ okay to feel sad for others. Seize the opportunity to talk about genetic screening that exists for certain populations for diseases like Sickle Cell disease.
End the discussion with a clip, “Beneficial mutations do happen”. This clip shows students that not all mutations are bad, which is generally a common misconception among students. The two views presented in the video clips helps students establish a balanced perspective about mutations and sets the stage for correct thinking about mutations as they relate to adaptations and evolution of species.
Display the Mutations Identification Problems. Explain that students will use the mRNA and amino acid sequences to identify the mutation that occurred and the effects of each one. Distribute copies of the same DNA sequences to students. Also, distribute copies of the mRNA decoder chart from the lesson, Protein Synthesis that are needed to help students associate the codons with the correct amino acids.
Explain that the activity requires students to first identify the mRNA and amino acid sequence for the original DNA sequence. Using a LCD projector, model this process with class participation. Students should be able to participate in this part of the activity because they learned how to sequence mRNA in the lesson, Protein Synthesis.
After that is done, model how to identify the mutation in the first mutated strand of DNA. Use the “think aloud” strategy so that students will be able to see the thought process used to identify the mutation type.
Mutated DNA Sequence #1: T A C A T C T T G G C G A C G A C T
What’s the mRNA sequence? (Circle the change)
What will be the amino acid sequence?
Will there likely be effects?
What kind of mutation is this?
Example Think Aloud script:
First, I need to break this strand of letters into codons by drawing line between each group of three letters because it will make it easier for me to track each codon when I identify the amino acid sequence. Next, I need to use the RNA base pair rule to match each nitrogen base with its complementary base. Let’s see. I think A goes with T. No, wait! I am building RNA, not DNA replication. In RNA T is replaced by U. So, A goes with U and C goes with G. Now that I have the RNA strand, let me use this amino acid codon sheet to identify the amino acid sequence. Let me compare this mutated sequence to the original sequence. Where is there a change? I need to look at each letter in the sequence to find the change, or error. I see it! A-C-C was changed to A-T-C. Because of that one letter, it changed the amino acid sequence. This is a point mutation, which will likely have effects because it changed the amino acid sequence.
Instruct students to work together to complete the remainder of the mutation problems. It’s important to note that independent practice does not always mean individual practice. This type of assignment is best completed with students collectively working together to learn and master the skill.
Share two best practices for students to use when working on this assignment:
- Separate the original DNA code into codons (triplets) before beginning the work of transcribing DNA into RNA. Use lines to separate the code into groups of three. This will help avoid the error of mis-reading code and it makes it easier to compare codon to codon when it is time to analyze the sequences to determine what type of mutation has occurred.
- After transcribing DNA into mRNA, compare codon to codon to identify exactly where the error has occurred and then, circle the error. Identify the type of error after this is done.
These two practices will help eliminate some of the confusion that typically occurs when students “lose” themselves in the code sequence and cannot correctly track the change because they are not sure exactly where in the code the change occurred.
The student work represents an exemplar of using the best practices described above. The student separates the DNA code into codons, and then follows the same practice when transcribing the DNA into mRNA. The amino acids are also separated and the place where the change in the sequence occurs is circled. There two simple actions will help students successfully complete this task.
While walking around, look for students’ use of these practices. Assist students as needed. If it appears that many students are stumped by the same problem, model the problem for the entire class, using the think aloud strategy so that students will be able to follow the thought process of how to identify DNA mutations.
Expect that this assignment will be a struggle for some. Be prepared to work with individual students or small groups of students to reinforce how to identify a mutation, beginning with the original DNA, to the mutated mRNA strand, and lastly to the protein.
Display the ticket out the door question. Engage students in a class discussion:
Why might a mutation of a sperm cell or egg cell have greater consequences than a mutation of a skin or lung cell?
Close the lesson by allowing students to share their thoughts. Make sure that students leave with correct reasoning and thinking. Look for students to identify that egg or sperm cells have greater consequence because the mutation can be passed on to offpspring that are produced from that egg or sperm cell.