Understanding Genetic Drift (Part 2 of 2)
Lesson 6 of 11
Objective: Students will use influenza as a model organism to understand genetic drift.
Using the data that students collected yesterday, students are able to see how genetic drift occurs and how it completes to natural selection. Since many of my students raise swine and poultry, there are many real-world application that can be drawn from this lesson for them. Here is is an overview of what students will learn today and why I use this method to teach the content.
Using the data collected from yesterday's activity, check for student understanding by having them share a way that they sorted their data. What patterns did they see in the data they collected?
(Note: Student responses can vary greatly depending on student comfort zone and experience sorting data. The majority of the students should have a list of the most commonly occurring variants. At the very least, they should have recognize when new viruses appear in the population and when viruses seem to drop out of the population. You may have students that start sorting data and then quit out of frustration or boredom. You could also see complete disaggregation of data where each variants is sorted within each species and the number of times each virus variant is tabulated. By the end of the lesson, the goal is to get everyone to the latter rather than the former. To do this requires some scaffolding for students which will be outlined in the lesson.)
Students should consider all of the pig viruses that were collected during yesterday's lesson. In the space provided on the student data sheet, they should record all of the possibilities of HA and NA proteins that were created. The first HA protein that appears in the population should be named HA1. Each subsequent HA protein should be named HA2, HA3, etc. The same naming protocol should be used of the naming of NA proteins replacing the HA with NA (e.g.: NA1).
Next, students should consider all of the duck viruses and record all of the possibilities of HA and NA proteins that were created. They should apply the same naming protocol to the HA and NA proteins to determine the names of the strains.
Finally, students should consider all of the variant human viruses and record all of the possibilities of HA and NA proteins that were created.
Students should count the number of strains the class created and record the data. They should list the types of strains and number of individual occurrences of each strain.
Ask students the following questions to check for understanding:
- Are any strains that are more common than others and tally them.
(Answers will vary depending on student data.)
- Reiterate how the mixing vessel hypothesis can explain antigenic shift.
(Possible answer: evolution can be defined as “changes in allele frequencies in a population over at least one generation”; it does not necessarily have to result in new species.)
- Should a new viral strain be considered a new species, and why or why not?
(Answers will vary, but students should be able to support their answers with evidence. Note: Students will have to revisit their assumptions about the species concept (phylogenetic, typological, or biological). They most often use biological species concept which refers to sexually reproducing, extant organisms. However, there are other species concepts.)
- “Using this definition of evolution, can antigenic shift be considered a mechanism for evolution?”
(Answer: Students should conclude that antigenic shift is definitely a mechanism for evolution as it is a specific example of natural selection at work.)
Determining the Vaccine
Students should sort their data and rank all the viruses in order of occurrence. Next, they should determine a rating system (i.e. rank the flu strain in order of last occurrence and number of occurrences). Finally, they should pick three flu strains for the vaccine. Encourage your students to determine if more data is needed to decide on any "ties" (i.e. mortality rate, contagiousness). Students should submit their recommendation(s) for the vaccine and give evidence why these were chosen.
Note: Consider this image of my students' white board sort. They chose to include five viruses in next year's vaccine. They requested more information about the number of pediatric deaths and number of complications due to the flu for the viruses that are circled. I liked their line of questioning so I made up some bogus data to help them in their determination.
Putting It All Together
In their lab notebooks, students will briefly summarize their recommendation for the vaccine. They should provide evidence to support their argument. (Note: typically students can determine one or two viruses to definitely place in next year's vaccine. However, they may ask for more information to determine what additional viruses should be included. It is up to the teacher's discretion to provide that data.)