Name: ______

Lesson 2: Genetics

Lesson 2: Testing Inheritance Models

1. Here are two models of how children inherit their traits from their parents. These models were proposed by students at your school. Read each model in pairs. With your partner, discuss which model is better. Give reasons why you think one is better than the other or why they are equally good or bad.

2. As a class, discuss the models and read evidence 1 together. Complete the arrow diagram together for trait #1.

3. Then in pairs, complete the arrow diagram for traits #2-#6.

4. When finished, discuss as a class.

Humans vary in their traits. Here are some examples of these traits:

Evidence 1: Sara and her parents

4. Some New Jersey middle school students were interested in understanding how people inherit their traits. To find out, they first randomly chose a person, Sara, in their class and recorded her traits. Sara went home that night and recorded her parents’ traits and brought her observations back to class the next day. Here are their results:

Sara / Sara's Father / Sara's Mother
Dimples / Dimples / Dimples
Unattached Earlobes / Unattached Earlobes / Unattached Earlobes
Widow's Peak / Widow's Peak / Straight Hairline
Curved Thumb / Straight Thumb / Curved Thumb
Can Roll Tongue / Can Roll Tongue / Can’t Roll Tongue
Can’t Taste PTC / Can Taste PTC / Can’t Taste PTC

5. In pairs talk about all the reasons why you are selecting each arrow. Make sure to discuss your ratings and arrows using the evidence and arrow stems.

Arrows Diagram

Trait / Strong Parent / Sex Model
Trait #1. Dimples
Sara / Dimples
Sara's Father / Dimples
Sara's Mother / Dimples
Trait #2. Earlobes
Sara / Unattached Earlobes
Sara's Father / Unattached Earlobes
Sara's Mother / Unattached Earlobes
Trait #3 Hairlines
Sara / Widow's Peak
Sara's Father / Widow's Peak
Sara's Mother / Straight Hairline
Trait #4 Thumbs
Sara / Curved Thumb
Sara's Father / Straight Thumb
Sara's Mother / Curved Thumb
Trait #5 Tongue Rolling
Sara / Can Roll Tongue
Sara's Father / Can Roll Tongue
Sara's Mother / Can’t Roll Tongue
Trait #6 Tasting PTC
Sara / Can’t Taste PTC
Sara's Father / Can Taste PTC
Sara's Mother / Can’t Taste PTC

6. As a pair, discuss whether any models can be ruled out by the evidence. Make sure to explain why a piece of evidence rules out a model.

7. View the slides about genes and traits.

8. Here are two more models of how children inherit their traits from their parents. These models were proposed by students in your class or other classes during the class discussion in Lesson 1. In pairs, read each model. With your partner, discuss which model is better.

9. Then in pairs, read Evidence 2 (below) and use evidence stems to discuss each piece of evidence. After discussing the evidence, fill in the arrows diagram on the next page.

Evidence 2: Teresa and her parents

10. Your teacher will introduce the two new models to you.

11. Sara, from Evidence 1, and Teresa are friends and they noticed that they have the same traits. Students wondered if Teresa’s parents have the same traits as Sara’s parents (shown in evidence 1). Here are their findings:

Teresa / Teresa's Father / Teresa's Mother
Dimples / No Dimples / Dimples
Unattached Earlobes / Unattached Earlobes / Unattached Earlobes
Widow's Peak / Widow's Peak / Straight Hairline
Curved Thumb / Straight Thumb / Curved Thumb
Can Roll Tongue / Can Roll Tongue / Can’t Roll Tongue
Can’t Taste PTC / Can Taste PTC / Can’t Taste PTC

12. As you discuss arrows, talk about all the reasons why you are selecting each arrow. Then in pairs discuss your arrows using the arrow stems.

Arrows Diagram

Trait / Strong Gene Model / Mixed Model
#1. Dimples
Teresa / Dimples
Teresa's Father / No Dimples
Teresa's Mother / Dimples
#2. Earlobes
Teresa / Unattached Earlobes
Teresa's Father / Unattached Earlobes
Teresa's Mother / Unattached Earlobes
#3 Hairlines
Teresa / Widow's Peak
Teresa's Father / Widow's Peak
Teresa's Mother / Straight Hairline
#4 Thumbs
Teresa / Curved Thumb
Teresa's Father / Straight Thumb
Teresa's Mother / Curved Thumb
#5 Tongue Rolling
Teresa / Can Roll Tongue
Teresa's Father / Can Roll Tongue
Teresa's Mother / Can’t Roll Tongue
#6 Tasting PTC
Teresa / Can’t Taste PTC
Teresa's Father / Can Taste PTC
Teresa's Mother / Can’t Taste PTC

13. In pairs, determine which model(s) can be ruled out by these pieces of evidence. Make sure to explain why a piece of evidence rules out a model.

14. Individually, answer this question. What is the best model of how children inherit traits from their parents? Why is this model the best model? Give reasons that show why this is the best model. Remember to use the model goodness criteria to help you construct your answer.

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15. As a class, discuss which model you think is the best, and explain why you think it is the best.

16. Check whether the best model can explain Evidence 1.

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