Download Name: Lesson 2: Genetics Lesson 2: Testing Inheritance Models 1

Name: _________________
Lesson 2: Genetics
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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.
MODEL 1: Strong Parent
MODEL 2: Sex Model
Text above says: The kids will get all of their
traits and things from the parent with the
stronger trait. So a mother whose traits are
stronger will give all of her genes to her son.
Text above says: Girls get traits from their
moms and boys get traits from their dads.
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.
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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
Dimples
Unattached Earlobes
Widow's Peak
Curved Thumb
Can Roll Tongue
Can’t Taste PTC
Sara's Father
Dimples
Unattached Earlobes
Widow's Peak
Straight Thumb
Can Roll Tongue
Can Taste PTC
Sara's Mother
Dimples
Unattached Earlobes
Straight Hairline
Curved Thumb
Can’t Roll Tongue
Can’t Taste PTC
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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.
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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.
MODEL 3: Strong Gene
MODEL 4: Mixed Model
Text above says: “Some genes are stronger
and some are weaker. So kids get genes from
their mom and dad. Whichever version of
the gene is stronger wins for that trait. So
you can get a strong version of a gene for one
trait from mom and a strong version of a
gene for a different trait from dad.
Text above says: “Every child gets genes
from mom and dad. The genes all get mixed
up together so that if dad is tall and mom is
short the kids will all be medium. Since they
mix there are no genes that are stronger
than any other genes.”
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
Dimples
Unattached Earlobes
Widow's Peak
Curved Thumb
Can Roll Tongue
Can’t Taste PTC
Teresa's Father
No Dimples
Unattached Earlobes
Widow's Peak
Straight Thumb
Can Roll Tongue
Can Taste PTC
Teresa's Mother
Dimples
Unattached Earlobes
Straight Hairline
Curved Thumb
Can’t Roll Tongue
Can’t Taste PTC
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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.
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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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