Monohybrid cross with incomplete dominance What phenotypic ratio is expected in the F2 generation when a trait shows incomplete dominance?

Introduction / Context:
Incomplete dominance occurs when the heterozygote phenotype is intermediate between the two homozygotes (e.g., red x white snapdragons producing pink F1). Understanding the resulting F2 ratios is foundational to classical genetics.

Given Data / Assumptions:

• Single gene with two alleles.
• Incomplete dominance: heterozygote has an intermediate phenotype.
• Random mating or selfing of F1 heterozygotes.

Concept / Approach:
From two true-breeding parents (AA and aa), F1 are all Aa and intermediate. Selfing F1 (Aa x Aa) yields genotypes AA, Aa, aa in a 1:2:1 ratio. With incomplete dominance, phenotypes mirror genotypes: 1 homozygote phenotype : 2 intermediate : 1 other homozygote.

Step-by-Step Solution:

Verification / Alternative check:
Classic examples (flower color) reproduce the 1:2:1 phenotypic ratio in lab crosses.

Why Other Options Are Wrong:

• 3:1:1 and 1:3:1 are not standard monohybrid outcomes.
• 1:1:2 misorders counts and is nonstandard.
• 9:3:3:1 applies to a dihybrid cross with independent assortment, not monohybrid.

Common Pitfalls:
Confusing incomplete dominance with codominance; both differ from strict dominance but have different phenotype interpretations.

Final Answer:
1:2:1