Mutations, part 2
Lesson 9 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: Why do you think low levels of mutation might be an adaptive advantage to a species, whereas high levels of mutation might be a disadvantage?
Engage students in a discussion around this review question from the previous lesson, Mutations, part 1. This question is a good question because it requires students to tie multiple biological concepts together to draw a conclusion.
To be sure that students understand the meaning of the term “adaptive advantage”, explain it to students. Remind students of the difference between adaptation and adjustment as discussed in the Characteristics of Life lesson, Life is for the Living.
Look for students to identify that low levels of mutation might benefit a species because the minor changes will likely allow the species to maintain life in the existing environment and possible better survive because of the minor changes. But, a high level of mutation might cause organisms to die or be so different that they can’t survive in the existing environment. This concept of adaptive advantage will segue into the Introduction of New Material.
Introduce New Material
- It is most common in people whose families come from Africa, South or Central America (especially Panama), Caribbean islands, Mediterranean countries (such as Turkey, Greece, and Italy), India, and Saudi Arabia.
- In the United States, it's estimated that sickle cell anemia affects 70,000–100,000 people, mainly African Americans. The disease occurs in about 1 out of every 500 African American births. Sickle cell anemia also affects Hispanic Americans. The disease occurs in more than 1 out of every 36,000 Hispanic American births.
- More than 2 million Americans have sickle cell trait. The condition occurs in about 1 in 12 African Americans. (source: NHLBI)
- Share two video clips with students to give them a perspective about the disease: Our story, Living and Managing Sickle Cell Disease, Nicholas and Tiffany.
Ask students to consider what populations at risk for sickle cell disease might have in common as it relates to the parts of the country or environments where their racial groups originate. Listen to students’ thoughts around this question. Look for students to identify that mosquitoes are more common in these environments. Be prepared to share this fact if students do not come up with it.
Note that individuals who are carriers for the sickle cell disease (with one sickle gene and one normal hemoglobin gene, also known as sickle cell trait) have some protective advantage against malaria. As a result, the frequencies of sickle cell carriers are high in malaria-endemic areas. (source, CDC).
Instruct students to engage in a 1 minute “turn and talk” with a seatmate to explain why then, given the information that has been shared, there are such high numbers of individuals with the disease or trait in the identified racial groups. Walk around to listen as students talk about why the incidence of the disease is so great in certain populations. Look for students to identify that the sickle blood cells are an example of an adaptive advantage in environments where mosquitoes thrive.
Given the student demographics, there may be several students in the class who have the disease or trait or who have members with the disease or train. Allow time for them to share their experiences with sickle cell disease, as they are comfortable.
Explain that students will demonstrate their understanding of the types of mutations through the use of drawings or sentences to show insertion, deletion, translocation and inversion.
Make sure that students understand that they should begin with a normal sentence or drawing that will serve as the template for the change or mutation that they are trying to demonstrate with words or images. Emphasize that the type of mutation must be identified in each sentence or drawing. Use a LCD projector to model how the process should occur.
Write a normal sentence:
THE BIG FAT CAT ATE THE WET RAT.
Model how deletion of one letter would change the sentence by eliminating the letter, B:
THE IGF ATC ATA TET HEW ETR AT
Point out how deletions change the sequence by shifting the letters. Explain that this is the reason deletions are also called frameshift mutations. Use of simple sentences should really help students see how mutations change a sequence of DNA.
Continue by modeling how to show an insertion mutation of the original sentence:
THE BIG ZFA TCA TAT ETH EWE TRA
And Translocation: ( add a 2nd sentence for translocation example, THE BOY SAT.)
THE BIG BOY SAT.
Walk around the room to monitor students’ work and ensure that all students are actively engaged in the completion of the task. Be prepared for some students to struggle with this assignment as it requires application of knowledge to creation of an independent work product and critical thinking skills.
Encourage students who are struggling with the assignment to use the sentence format to demonstrate content mastery because the use of sentences is not as abstract a skill as drawing images to convey depth of understanding, which is a higher level application of the content knowledge. For example, student work 2 conveys understanding using sentences.
Encourage students to use creative ways to demonstrate their understanding of what occurs after the different types of mutation. Student work 1 and student work 4 both show how students are able to graphically depict each of the different types of mutations. Each is different in how ther represent the mutations but both are correct. student work 3 shows a student who is able to show understanding graphically and using sentences. The ability of all students to complete this assignment in a manner that conveys accurate depiction of the types pf mutations reflects mastery of the concept.
Ask the question, “What is one concept or thought about mutations has “stuck” with you? Distribute post-it notes and allow students to write one idea on the note. Instruct students to place the notes on a chart pad before leaving the classroom.