OSMIA LEARNING · GENETICS

Punnett Square Practice

Topic: Monohybrid inheritance Grade band: 7–10 NGSS*: MS-LS3-2, HS-LS3-3

Name: Date: Period:

Vocabulary Determine genotypes Build the square Predict ratios Interpret & reason

Part A — Vocabulary & genotypes Vocabulary · Determine genotypes

1. In rabbits, black fur (B) is dominant over brown fur (b). Write the genotype for each rabbit described.

a. Homozygous black: b. Heterozygous black: c. Brown:

2. A pea plant has white flowers. White (p) is recessive to purple (P). What must its genotype be, and how do you know?

3. Define each term in your own words:

Genotype:

Phenotype:

Part B — Build the square Build the square · Predict ratios

4. Cross two heterozygous black rabbits (Bb × Bb). Complete the Punnett square, then answer below.

	B	b
B
b

Genotype ratio: Phenotype ratio (black : brown):

5. Cross a heterozygous black rabbit with a brown rabbit (Bb × bb). Complete the square and give the predicted percent of brown offspring.

	b	b
B
b

Percent brown offspring:

* NGSS is a registered trademark of WestEd. Neither WestEd nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it. NGSS Lead States. 2013. Next Generation Science Standards: For States, By States. Washington, DC: The National Academies Press.

Part C — Predict & reason Predict ratios · Interpret & reason

6. A homozygous purple-flower pea plant (PP) is crossed with a white-flower plant (pp). Build the square. What genotype and phenotype do all offspring share?

	p	p
P
P

All offspring genotype: phenotype:

7. From the cross in #4 (Bb × Bb), a breeder raises 4 baby rabbits and none are brown. Did the breeder do something wrong? Explain using the idea of probability.

8. Test cross. A black rabbit could be BB or Bb. Describe a single cross that would reveal which genotype it has, and explain what result would tell you it is Bb.

9. Challenge. In guinea pigs, a Bb × Bb cross is expected to give a 3 : 1 phenotype ratio. Explain why two heterozygous black parents can still produce a brown offspring.