Exploratorium: Why Don't Brothers and Sisters Look Exactly Alike?

Family Similarities Brainstorm
Display photographs of several families.

Ask students:

• What similarities do you notice between parents and children?
• What differences do you notice?
• Why do you think family members look alike?
• Why don't brothers and sisters look the same?

Students discuss with a partner and then share with the class.

Record responses without judging whether they are correct.

Teacher Tip
Accept all observations and ideas. The goal is to uncover students' current thinking about inheritance and variation rather than immediately teaching the correct answer.

Introduce the Phenomenon
Present the guiding question:

"Why is there so much variation within families?"

Explain that scientists have studied this question for hundreds of years.

Today, students will investigate how traits are influenced by:

• Genes
• Environment
• The interaction between genes and environment

Introduce key vocabulary:

• Trait
• Inheritance
• Gene
• Variation
• Environment

Ask:

"What are some traits that run in families?"

Examples may include:

• Eye color
• Hair color
• Height
• Skin color
• Dimples

Activity 1: Developing an Initial Model
Place students into small groups.

Provide each group with family photographs.

Students answer:

1. What similarities do you see?
2. What differences do you see?
3. What might explain these similarities?
4. What might explain these differences?

Groups create a simple model showing how they think traits are passed from parents to children.

Students may use:

• Drawings
• Diagrams
• Arrows
• Labels

Guiding Questions

• What causes family members to resemble one another?
• Why are siblings different?
• What information is missing from your model?

Groups briefly share their models.

Teacher Tip
Ask probing questions rather than supplying answers.

Examples:

• What does this arrow represent?
• How does this factor influence the trait?
• Could anything besides genes affect the trait?

Activity 2: Genetics vs. Environment Spectrum
Place signs around the room:

GENETICS ←——————————→ ENVIRONMENT

Read a series of traits aloud.

Students place a sticky note where they believe each trait belongs on the spectrum.

Suggested traits:

• Height
• Skin color
• Athletic ability
• Hair color
• Language spoken
• Weight
• Musical ability
• Eye color

After each placement, discuss:

• Why did you place your note there?
• Could both genes and environment influence this trait?
• Which traits seem mostly genetic?
• Which seem mostly environmental?

Key Understanding

Most human traits are influenced by both genes and environmental factors working together.

Exit Ticket
Students respond to the following questions:

1. Why do siblings look similar to one another?
2. Why don't siblings look exactly alike?
3. Name one trait influenced mostly by genes.
4. Name one trait influenced by both genes and environment.

Success Criteria
Students can:

✓ Explain that traits are inherited through genes.

✓ Recognize that environmental factors affect many traits.

✓ Describe why variation exists within families.

Revise Your Original Model
Return students' original models.

Ask students to revise them using what they learned during the lesson.

Students should add:

• New information
• New labels
• New connections
• Environmental influences

Reflection Prompt
Write a short paragraph:

"How has your explanation of family resemblance changed since the beginning of today's lesson?"

Students cite evidence from class discussions and activities.