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Punnett Square worksheet

Grades 7–8 · CCSS 7.SP.C.8.b

Solve each problem and show your work. Round answers to 2 decimal places where needed.

1.
Problem 1.
- Cross: Dihybrid (two genes)
- Parent 1, gene A: AA
- Parent 2, gene A: Aa
- Parent 1, gene B: bb
- Parent 2, gene B: bb
Find: Phenotype ratio
Answer
2.
Problem 2.
- Cross: Monohybrid (one gene)
- Parent 1, gene A: Aa
- Parent 2, gene A: aa
Find: Phenotype ratio
Answer
3.
Problem 3.
- Cross: Monohybrid (one gene)
- Parent 1, gene A: aa
- Parent 2, gene A: Aa
Find: Phenotype ratio
Answer
4.
Problem 4.
- Cross: Monohybrid (one gene)
- Parent 1, gene A: AA
- Parent 2, gene A: Aa
Find: Phenotype ratio
Answer
5.
Problem 5.
- Cross: Monohybrid (one gene)
- Parent 1, gene A: AA
- Parent 2, gene A: AA
Find: Phenotype ratio
Answer
6.
Problem 6.
- Cross: Dihybrid (two genes)
- Parent 1, gene A: aa
- Parent 2, gene A: AA
- Parent 1, gene B: bb
- Parent 2, gene B: Bb
Find: Phenotype ratio
Answer
7.
Problem 7.
- Cross: Dihybrid (two genes)
- Parent 1, gene A: aa
- Parent 2, gene A: AA
- Parent 1, gene B: bb
- Parent 2, gene B: BB
Find: Phenotype ratio
Answer
8.
Problem 8.
- Cross: Monohybrid (one gene)
- Parent 1, gene A: Aa
- Parent 2, gene A: AA
Find: Phenotype ratio
Answer
9.
Problem 9.
- Cross: Dihybrid (two genes)
- Parent 1, gene A: aa
- Parent 2, gene A: AA
- Parent 1, gene B: bb
- Parent 2, gene B: bb
Find: Phenotype ratio
Answer
10.
Problem 10.
- Cross: Monohybrid (one gene)
- Parent 1, gene A: AA
- Parent 2, gene A: aa
Find: Phenotype ratio
Answer

Answer key: Punnett Square worksheet

1. Phenotype ratio: All A_bb
1. List each parent's gametes. Each one carries one allele of each gene, and every combination is equally likely
  $AAbb → Ab, Ab, Ab, Ab; Aabb → Ab, Ab, ab, ab$
2. Pair every gamete of parent 1 with every gamete of parent 2. Each pair fills one box
  $4 \times 4$ $= 16$
3. Count each genotype in the 16 boxes, then shrink the ratio to its smallest whole numbers
  $1 AAbb : 1 Aabb$
4. Group boxes by visible trait. One dominant allele is enough to show the dominant trait, and _ stands for either allele
  $All A_bb$
5. Chance of the A_bb trait: its boxes out of all the boxes
  $\frac{16}{16}$ $= 100%$
2. Phenotype ratio: 1 A_ : 1 aa
1. List each parent's gametes. Each parent passes on one of its two alleles, with equal chance
  $Aa → A, a; aa → a, a$
2. Pair every gamete of parent 1 with every gamete of parent 2. Each pair fills one box
  $2 \times 2$ $= 4$
3. Count each genotype in the 4 boxes, then shrink the ratio to its smallest whole numbers
  $1 Aa : 1 aa$
4. Group boxes by visible trait. One dominant allele is enough to show the dominant trait, and _ stands for either allele
  $1 A_ : 1 aa$
5. Chance of the A_ trait: its boxes out of all the boxes
  $\frac{2}{4}$ $= 50%$
6. Chance of the aa trait: its boxes out of all the boxes
  $\frac{2}{4}$ $= 50%$
3. Phenotype ratio: 1 A_ : 1 aa
1. List each parent's gametes. Each parent passes on one of its two alleles, with equal chance
  $aa → a, a; Aa → A, a$
2. Pair every gamete of parent 1 with every gamete of parent 2. Each pair fills one box
  $2 \times 2$ $= 4$
3. Count each genotype in the 4 boxes, then shrink the ratio to its smallest whole numbers
  $1 Aa : 1 aa$
4. Group boxes by visible trait. One dominant allele is enough to show the dominant trait, and _ stands for either allele
  $1 A_ : 1 aa$
5. Chance of the A_ trait: its boxes out of all the boxes
  $\frac{2}{4}$ $= 50%$
6. Chance of the aa trait: its boxes out of all the boxes
  $\frac{2}{4}$ $= 50%$
4. Phenotype ratio: All A_
1. List each parent's gametes. Each parent passes on one of its two alleles, with equal chance
  $AA → A, A; Aa → A, a$
2. Pair every gamete of parent 1 with every gamete of parent 2. Each pair fills one box
  $2 \times 2$ $= 4$
3. Count each genotype in the 4 boxes, then shrink the ratio to its smallest whole numbers
  $1 AA : 1 Aa$
4. Group boxes by visible trait. One dominant allele is enough to show the dominant trait, and _ stands for either allele
  $All A_$
5. Chance of the A_ trait: its boxes out of all the boxes
  $\frac{4}{4}$ $= 100%$
5. Phenotype ratio: All A_
1. List each parent's gametes. Each parent passes on one of its two alleles, with equal chance
  $AA → A, A; AA → A, A$
2. Pair every gamete of parent 1 with every gamete of parent 2. Each pair fills one box
  $2 \times 2$ $= 4$
3. Count each genotype in the 4 boxes, then shrink the ratio to its smallest whole numbers
  $All AA$
4. Group boxes by visible trait. One dominant allele is enough to show the dominant trait, and _ stands for either allele
  $All A_$
5. Chance of the A_ trait: its boxes out of all the boxes
  $\frac{4}{4}$ $= 100%$
6. Phenotype ratio: 1 A_B_ : 1 A_bb
1. List each parent's gametes. Each one carries one allele of each gene, and every combination is equally likely
  $aabb → ab, ab, ab, ab; AABb → AB, Ab, AB, Ab$
2. Pair every gamete of parent 1 with every gamete of parent 2. Each pair fills one box
  $4 \times 4$ $= 16$
3. Count each genotype in the 16 boxes, then shrink the ratio to its smallest whole numbers
  $1 AaBb : 1 Aabb$
4. Group boxes by visible trait. One dominant allele is enough to show the dominant trait, and _ stands for either allele
  $1 A_B_ : 1 A_bb$
5. Chance of the A_B_ trait: its boxes out of all the boxes
  $\frac{8}{16}$ $= 50%$
6. Chance of the A_bb trait: its boxes out of all the boxes
  $\frac{8}{16}$ $= 50%$
7. Phenotype ratio: All A_B_
1. List each parent's gametes. Each one carries one allele of each gene, and every combination is equally likely
  $aabb → ab, ab, ab, ab; AABB → AB, AB, AB, AB$
2. Pair every gamete of parent 1 with every gamete of parent 2. Each pair fills one box
  $4 \times 4$ $= 16$
3. Count each genotype in the 16 boxes, then shrink the ratio to its smallest whole numbers
  $All AaBb$
4. Group boxes by visible trait. One dominant allele is enough to show the dominant trait, and _ stands for either allele
  $All A_B_$
5. Chance of the A_B_ trait: its boxes out of all the boxes
  $\frac{16}{16}$ $= 100%$
8. Phenotype ratio: All A_
1. List each parent's gametes. Each parent passes on one of its two alleles, with equal chance
  $Aa → A, a; AA → A, A$
2. Pair every gamete of parent 1 with every gamete of parent 2. Each pair fills one box
  $2 \times 2$ $= 4$
3. Count each genotype in the 4 boxes, then shrink the ratio to its smallest whole numbers
  $1 AA : 1 Aa$
4. Group boxes by visible trait. One dominant allele is enough to show the dominant trait, and _ stands for either allele
  $All A_$
5. Chance of the A_ trait: its boxes out of all the boxes
  $\frac{4}{4}$ $= 100%$
9. Phenotype ratio: All A_bb
1. List each parent's gametes. Each one carries one allele of each gene, and every combination is equally likely
  $aabb → ab, ab, ab, ab; AAbb → Ab, Ab, Ab, Ab$
2. Pair every gamete of parent 1 with every gamete of parent 2. Each pair fills one box
  $4 \times 4$ $= 16$
3. Count each genotype in the 16 boxes, then shrink the ratio to its smallest whole numbers
  $All Aabb$
4. Group boxes by visible trait. One dominant allele is enough to show the dominant trait, and _ stands for either allele
  $All A_bb$
5. Chance of the A_bb trait: its boxes out of all the boxes
  $\frac{16}{16}$ $= 100%$
10. Phenotype ratio: All A_
1. List each parent's gametes. Each parent passes on one of its two alleles, with equal chance
  $AA → A, A; aa → a, a$
2. Pair every gamete of parent 1 with every gamete of parent 2. Each pair fills one box
  $2 \times 2$ $= 4$
3. Count each genotype in the 4 boxes, then shrink the ratio to its smallest whole numbers
  $All Aa$
4. Group boxes by visible trait. One dominant allele is enough to show the dominant trait, and _ stands for either allele
  $All A_$
5. Chance of the A_ trait: its boxes out of all the boxes
  $\frac{4}{4}$ $= 100%$