In a monohybrid cross between two heterozygous individuals (Aa × Aa), the phenotypic ratio of offspring is:

## The Reasoning When you cross **Aa × Aa**, think of it as mixing possibilities. Each parent can give either **A** (dominant) or **a** (recessive). Using a **Punnett square**: - **AA** (1 out of 4) → Shows dominant trait - **Aa** (2 out of 4) → Shows dominant trait (because A masks a) - **aa** (1 out of 4) → Shows recessive trait So **genotypic ratio** = 1 AA : 2 Aa : 1 aa But **phenotypic ratio** (what you *see*) groups them differently: - **Dominant phenotype** (AA + Aa) = 3 - **Recessive phenotype** (aa) = 1 **Answer: 3:1** This is **Mendel's Law of Dominance** in action. --- ## Why the Wrong Options Tempt You **A) 1:1** — That's a *test cross* (Aa × aa), not heterozygous × heterozygous. **C) 1:2:1** — You're looking at *genotypes*, not phenotypes! Don't fall for it. **D) 9:3:3:1** — That's a *dihybrid* cross (two traits), not monohybrid (one trait). --- ## Quick Takeaway **Heterozygous monohybrid = 3:1 phenotype.** Dominant masks recessive, so three show dominant, one shows recessive. Simple!