Grade 9life scienceOriginal practice

Use a Simple Inheritance Model

Interpret a one-gene complete-dominance model without overgeneralizing. A complete set with exploration, practice and application. Use the linked unit for the learning sequence and teaching guide.

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Independent activity · About 25 minutes · Pencil · Biology

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Grade 9 · science

Use a Simple Inheritance Model

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Grade 9 · science · continued

Use a Simple Inheritance Model

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An illustrative allele model

In a simplified model, A is dominant and a is recessive. Two Aa parents each contribute A or a with equal chance. The model assumes complete dominance and does not describe every real trait.

Use the material to work through each task. Show the requested response.

1.How many boxes show Aa?

2.What probability does the model give for aa?

3.What probability has at least one A?

4.Name the two homozygous genotypes shown.

5.Does the model guarantee one aa child in every four?

6.Does dominant mean the allele must be most common?

Grade 9 · science · Answer key

Use a Simple Inheritance Model

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Open responses use criteria and an illustrative response. Other well-supported responses can be acceptable.

Grade 9 · science · Answer key · continued

Use a Simple Inheritance Model

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An illustrative allele model

In a simplified model, A is dominant and a is recessive. Two Aa parents each contribute A or a with equal chance. The model assumes complete dominance and does not describe every real trait.

Use the material to work through each task. Show the requested response.

1.How many boxes show Aa?

Answer: 2

2.What probability does the model give for aa?

Answer: 1/4

3.What probability has at least one A?

Answer: 3/4

4.Name the two homozygous genotypes shown.

Answer: AA and aa

5.Does the model guarantee one aa child in every four?

Look for

Distinguishes probability from guarantee.

One possible response: No. It represents probabilities, not a fixed family outcome.

6.Does dominant mean the allele must be most common?

Look for

Does not equate dominance with frequency.

One possible response: No. Dominance describes expression in this model, not population frequency.

About this practice

Grade 9 · science · Matching answer key included · US Letter and A4

US Letter practice PDF ↓ · Answer PDF ↓A4 practice PDF ↓ · Answer PDF ↓

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Use a Simple Inheritance Model: first student practice page

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Teaching guide, sample answers and curriculum references

Before you begin

Review the key words and representations in Use a Simple Inheritance Model. Use the Explore activity to check readiness before removing support.

How to use this worksheet

Begin with: How many boxes show Aa?
Connect the response to: What probability has at least one A?
Ask students to apply the idea: Does the model guarantee one aa child in every four?

A common mistake to discuss

Accepting an answer without checking whether it uses the material and satisfies the requested relationship or criteria.

What to practice next

Continue to Use a Simple Inheritance Model: Apply and Create.

Original instructional material written for this practice.

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Published 2026-10-04; updated 2026-10-04. Original MakeWorksheet practice. Automated consistency checks support publication; independent subject-specialist review is not recorded. Read our editorial policy.

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Use a Simple Inheritance Model: Apply and Create: first student practice page

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Grade 9

Key

Use a Simple Inheritance Model: Apply and Create

Apply · Independent · 15 min

Interpret a one-gene complete-dominance model without overgeneralizing. A focused apply activity. Use the linked unit for the learning sequence and teaching guide.

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Use a Simple Inheritance Model: Explore and Explain: first student practice page

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Grade 9

Key

Use a Simple Inheritance Model: Explore and Explain

Explore · Independent · 10 min

Interpret a one-gene complete-dominance model without overgeneralizing. A focused learn activity. Use the linked unit for the learning sequence and teaching guide.

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Use a Simple Inheritance Model: Practice Independently: first student practice page

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Grade 9

Key

Use a Simple Inheritance Model: Practice Independently

Practice · Independent · 10 min

Interpret a one-gene complete-dominance model without overgeneralizing. A focused practice activity. Use the linked unit for the learning sequence and teaching guide.

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High School Biology: Mendelian Genetics & Punnett Squares: first student practice page

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Grade 9

NGSS.HS-LS3-2 Key

High School Biology: Mendelian Genetics & Punnett Squares

Practice · Independent · 15 min

Calculate phenotypic and genotypic probabilities, analyze monohybrid and dihybrid crosses, and apply Mendel's laws of inheritance with diagrams.

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