Comparative DNA - Evidence for Evolution
Lesson 9 of 15
Objective: SWBAT construct an explanation for how similarities in DNA sequences across species is evidence for evolution.
In this section of lesson I engage students by showing them the picture below. This picture shows the genetic sequences of two species of butterflies and 2 species of owls.
This has been a whole new area of evolution research looking at the drift in genes over time as a way of determining the age of species since they "separated" from a common ancestor age of species since they "separated" from a common ancestor.
(MS-LS4-2 - Apply scientific ideas to construct an explanation for the anatomical similarities and differences among modern and fossil organisms to infer evolutionary relationships./CCC - Patterns - Graphs, charts, and images can be used to identify patterns in data.)
Once students have looked at picture closely, I have students discuss with their group members the following sequences:
1. Based on the DNA sequences pictured above what 2 species would you say are more closely related? Please explain.
2. Based on the DNA sequences pictured above what 2 species would you say are least closely related? Please explain.
3. Based on the DNA sequences pictured above would you say that butterflies and owls are closely related? Please explain.
I use RallyRobin (mastery, thinking, communication) as the strategy for this discussion. In pairs, students alternate generating oral responses.
Teacher poses a problem to which there are multiple possible responses or solutions.
In pairs, students take turns stating responses or solutions orally.
In this section, we explore comparative DNA analysis. I start this section by showing students a graph that shows the number of amino acids that differ from a human hemoglobin polypeptide.
The objective of this graph is to communicate the inverse relationship between difference in number of amino acids and the genetic relatedness between species. (CCC - Patterns - Graphs, charts, and images can be used to identify patterns in data./SP4 - Analyzing and Interpreting Data)
I have student write their answers to the following questions:
1. According to graph what species are humans furthest related to? What information did you use from the graph to answer question.
2. As the difference in number of amino acids increases what happens to the genetic relatedness between two species.
3. Humans share a closer related common ancestor with which animal? What evidence did you use to make this claim.
Once student have had time to answer and discuss the questions, I hand out DNA sequences to complete the following activity:
Educational Goal: Have participants observe, using actual DNA sequence, that conserved DNA is very similar across species.
Once students have completed activity they answer the following questions:
- Which sequence is more conserved, has changed less, during evolution? Which sequence do you think is more important?
- How many of you are surprised that there are sequences of DNA like this that we have that are almost identical to those in a chicken? Turns out, some DNA sequence is so important that every single living thing has it, from people to plants, and bacteria.
Now, students read an article titled Molecular Evidence for Evolution from cK-12, using the Writing in the Margins strategy to interact with text.
Writing in the margins engages readers in the reading task and allows them to document their thinking while reading. Both writing in the margins and drawing in the margins engages students in actively thinking about the texts they read. The power of this strategy is not the actual act of writing and drawing in the margins; instead, it is the thinking processes that students must undergo in order to produce such ideas.
Students use the Respond strategy, which is explained in my reflection.
Once students have read the article, they answer the following questions: (WHST.6.8.9 - Draw evidence from informational texts to support analysis, reflection, and research.)
- Explain how scientists use a molecular clock to determine relationships between species.
- What is a genome?
- What two species from the following should have the fewest differences in their genomes: chicken, mouse, duck, gorilla?
- What two species from the following should have the most differences in their genomes: frog, mouse, cow, human?
In addition to reading the article, I show students two videos from The Shape of Life and have them answer the questions below.
Genes Tell Us About Evolution
- How is the genetic sequence of an organism like a blueprint of that organism?
- If two organisms have almost identical sequences for the same gene, are they considered closely related?
- What type of animal have scientists long thought was basal to all other animals? How has genetic analysis affected this view?
- How has genetic analysis become quicker than it once was? How has that greatly helped with the search for a basal organism?
How Genes Direct Development
- What is a regulatory gene? How might they explain differences between organisms?
- What are "hox genes"? What phase of development are they a part of? What organisms have hox genes?
- If you find a fly with a leg coming out of its head and can identify what happened genetically to cause this, what have you discovered?
In this section, students read an article titled DNA Proves Evolution written by Steve Potter, PhD, a Professor of Pediatrics, in the Division of Developmental Biology at Children’s Hospital Medical Center in Cincinnati.
Students conduct a Close Reading of this article.
Once students have completed close reading, students answer the following text dependent questions. (WHST.6.8.9 - Draw evidence from informational texts to support analysis, reflection, and research.)
1. How did the Human Genome project get scientists closer to answer the question of what makes us most people so different from each other?
2. What was one of the most incredible discoveries to come from the Human Genome Project?
3. What are some examples the author uses to communicate his feeling of being amazed that we have a "pitifully puny number?"
4. Our individual differences come from what percentage of our DNA sequence?
5. What does the author mean by "mouse and man are 99% genetically identical."
6. Cite evidence from article that supports the claim that they fly and human genes appeared to be functionally equivalent.
Using evidence from today's lesson, students construct a scientific explanation from an excerpt from the article Protein links T.Rex to Chickens from the BBC. (SP6 - Constructing Explanations and Designing Solutions)
In other words, "Why is obtaining DNA sequences from extinct organisms a long-standing goal to test evolutionary links."
Brooks Hanson, an editor at Science journal said: "The goal of obtaining sequences either from proteins or DNA for extinct [organisms] has been a long-standing goal to test evolutionary links and processes, or even functional information."