1.In pea plants, purple flowers (P) are completely dominant over white flowers (p). If two heterozygous purple-flowered plants (Pp × Pp) are crossed, what percentage of their offspring is predicted to display white flowers?
A0%
B25%
C50%
D75%
Grade 9life scienceOriginal practice
High School Biology: Mendelian Genetics & Punnett Squares
Calculate phenotypic and genotypic probabilities, analyze monohybrid and dihybrid crosses, and apply Mendel's laws of inheritance with diagrams.
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About this practice
Grade 9 · science · Matching answer key included · US Letter and A4
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Teaching guide, sample answers and curriculum references
Before you begin
Identify alleles and distinguish genotype from phenotype in a simple inheritance model.
How to use this worksheet
- Model the target skill: predict genotypic and phenotypic ratios in monohybrid crosses using Punnett square probability models. Use the first task as a guided example before asking for an independent response.
- Check readiness first: Identify alleles and distinguish genotype from phenotype in a simple inheritance model.
- Discuss an incorrect response using this distinction: A Punnett square gives possible outcomes and probabilities, not a guaranteed sequence of children.
A common mistake to discuss
A Punnett square gives possible outcomes and probabilities, not a guaranteed sequence of children.
What to practice next
Explain a probability using the parental allele combinations in the square.
Sample question and answer
In pea plants, purple flowers (P) are completely dominant over white flowers (p). If two heterozygous purple-flowered plants (Pp × Pp) are crossed, what percentage of their offspring is predicted to display white flowers?
- A. 0%
- B. 25%
- C. 50%
- D. 75%
Answer: B. A Pp × Pp Punnett square produces: 1 PP (purple), 2 Pp (purple), 1 pp (white). The homozygous recessive pp genotype represents 1 out of 4 (25%) of offspring.
Intended curriculum references: NGSS.HS-LS3-2 · NGSS.HS-LS3-3. These references describe learning goals; they are not endorsements.
Published 2026-10-02; updated 2026-10-02. Original MakeWorksheet practice. Automated consistency checks support publication; independent subject-specialist review is not recorded. Read our editorial policy.
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