What Makes Me Unique?
Humans are more alike than we are different. It comes down to our DNA. In this lesson, students will see DNA and learn how it makes up their physical traits. They will learn how their DNA makes them unique and what they share with all other humans.
Time:
40 Mins.Grade: 1-5 Grade
Objectives
- Students will extract DNA from a strawberry to learn about their own cells.
- They will discuss what makes them different and similar to other humans.
Summary
Humans are 99.9% similar to each other genetically. What makes us unique? In this lesson, students will discover the molecule that gives them their physical characteristics. DNA is a molecule found in all living things. It is the recipe for creating all our physical traits. Humans have two copies of DNA, one from each parent. Some fruits, like strawberries, have more copies of DNA. Using a strawberry, students can pull the DNA out of the fruit to see with the naked eye.
Lesson
Teacher Preparation
Print a copy for each student of the What Makes Me Unique Lab Notebook.
Strawberry DNA set up (Tip: Use the Strawberry DNA Extraction printable at home or in class to help with instructions.)
- Make sure strawberries are at room temperature and rubbing alcohol is frozen (on ice).
- Place 1 strawberry in a sealable plastic bag. You need 1 per student.
Create the extraction buffer
- For 26 students: Mix ½ cup of dish or hand soap, 6-½ cups of water and ¼ cup salt together. Stir well.
- For 1 student: Mix 1 teaspoon of dish or hand soap, ¼ cup of water and ½ teaspoon of salt. Stir well.
This will be provided to students in a cup or test tube during the lesson.
Lesson Plan
Using the What Makes Me Unique? Slide Show, show students the photos of fruits. Use think-pair-share to discuss the similarities and differences of the fruits in the picture. Think: Students write individually in their What Makes Me Unique Lab Notebook; pair: Students share what they wrote with their neighbor; share: students share with the class.
Have students talk to their neighbor to decide how they are the same and how they are different. Ask students to brainstorm what makes them who they are.
Experiment Time! Strawberry DNA Extraction
Give each student a strawberry in a bag. Make sure the bag is tightly sealed. Have students gently smash the strawberry until it is crushed. This starts the process of breaking the cells so DNA is released. Tip: If you would like to show students the process or share with families at home, use this video: Can You Pull DNA From a Strawberry?
Provide students with ¼ cup of the premade extraction buffer. If you did not make the extraction buffer ahead of time, you can make it now.
Note: The dish or hand soap breaks down the cell membrane and allows the DNA out. The salt helps to remove the protein wound in the DNA.
Add the extraction buffer to the plastic bag with the strawberries. This will break down the cells even more.
Reseal the bag. Be sure that the bag is fully sealed! Have students gently massage the strawberry liquid. Remind students to try not to make too many bubbles.
Ask students to place a coffee filter on top of a funnel and put the funnel into the other cup. Have a partner hold the filter in place as they pour the strawberry mixture in. Be sure it does not overflow.
Allow the strawberry juice to run into the cup. Twist the top of the filter just above the juice and gently squeeze the remaining liquid into the cup.
Students should remove the filter. Pour ¼ cup of ice cold rubbing alcohol down the side of the cup. Do not mix! You and your students have isolated DNA from the cell. It will slowly start to precipitate.
Note: The DNA is dissolved within the water but when cold alcohol is added the DNA falls out of the solution and clumps up.
Watch for a white cloudy substance to form in the alcohol layer. This is the strawberry’s DNA. Using a coffee stirrer or craft stick, students can slowly stir the top layer, and then, pull out the DNA!
Discussion
Discuss how the stringy substance is DNA. Through this procedure, students were able to isolate the DNA and make it clump together.
DNA is found in every living thing. It is the recipe, or genetic instructions, for how to make all physical characteristics. Humans have two copies of DNA, one from each parent. It is important to help students understand how their DNA is in their cells. Strawberries are great for isolating DNA because they are octoploid. They have eight copies of DNA; whereas, humans only have two copies.
Discuss the structure of DNA. You can use the DNA Coloring Page to help explain the structure and identify base pairs. It is built of smaller parts that give DNA a unique code. It can be compared to building a tower of blocks. Everyone’s structure is just a little bit different but made of the same basic pieces.
Extend the Lesson: If you have time, use pipe cleaners and beads to build their own DNA models with this DNA Building Activity.
The Sanford Connection
Your genes determine certain traits, like your eye color or or hair texture. They also affect your risk of certain health conditions that can be passed down from your family. Understanding your genes can help you and your family make medical decisions. At Sanford Imagenetics, doctors and specialists can use genetic testing to help patients understand disease. Learn more about genetic testing on a podcast featuring Cassie Hajek, MD.
Did you try this lesson? Tell us about your experience.
Materials
Per student:
- 1 fresh or frozen strawberry (thawed)
- 1 sealable plastic bag
- 2 cups
- 1 coffee filter or cheesecloth
- 1 funnel
- 1 stir stick
- ¼ cup of ice cold rubbing alcohol
- Extraction buffer:
- 1 teaspoon of dish or hand soap per student (½ cup for 26 students)
- ¼ cup of water (6-½ cups for 26 students)
- ½ teaspoon of salt (¼ cups for 26 students)
Performance Expectations
Science & Engineering Practices
- Asking questions and defining problems
- Planning and carrying out investigations
- Analyzing and interpreting data