Monohybrid Crosses - Story Problems - Free Printable

Let’s work through each of the 4 monohybrid cross problems step by step.

We’re told:
- T = tall (dominant)
- t = short (recessive)

That means:
- TT or Tt → tall plant
- tt → short plant

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Problem 1: A homozygous tall plant is crossed with a heterozygous plant. What are the ratios?

Homozygous tall = TT
Heterozygous = Tt

Set up Punnett square:

| T | T
--|-----|-----
T | TT | TT
t | Tt | Tt

Genotypes:
→ 2 TT : 2 Tt → which simplifies to 1:1 ratio (TT : Tt)
Or we can say: 50% TT, 50% Tt

Phenotypes:
All offspring have at least one T → all are tall
→ 100% tall

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Problem 2: If a homozygous recessive plant is crossed with a homozygous tall plant, what will the offspring be like?

Homozygous recessive = tt
Homozygous tall = TT

Punnett square:

| T | T
--|-----|-----
t | Tt | Tt
t | Tt | Tt

Genotypes:
All are Tt → 100% heterozygous

Phenotypes:
All have T → all are tall → 100% tall

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Problem 3: If a heterozygous plant is crossed with a homozygous recessive plant, what will the offspring be like?

Heterozygous = Tt
Homozygous recessive = tt

Punnett square:

| t | t
--|-----|-----
T | Tt | Tt
t | tt | tt

Genotypes:
2 Tt : 2 tt → 1:1 ratio (Tt : tt)
Or 50% Tt, 50% tt

Phenotypes:
Tt → tall
tt → short
→ 50% tall, 50% short

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Problem 4: If two homozygous recessive plants are crossed, what will the children be like?

Both parents = tt

Punnett square:

| t | t
--|-----|-----
t | tt | tt
t | tt | tt

Genotypes:
All are tt → 100% homozygous recessive

Phenotypes:
All are short → 100% short

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Final Answer:

1. Genotypes: 1 TT : 1 Tt; Phenotypes: 100% tall
2. Genotypes: 100% Tt; Phenotypes: 100% tall
3. Genotypes: 1 Tt : 1 tt; Phenotypes: 50% tall, 50% short
4. Genotypes: 100% tt; Phenotypes: 100% short