Video narration
Working out inheritance odds without a Punnett square can feel like guesswork. But a monohybrid cross-one trait-is simple to solve mentally: Aa times Aa. Each parent passes one allele, A or a, with equal chances. Think fair coin: A on one side, a on the other. It models the choice, not literal inheritance. Now pair the choices. A with A makes AA. A with a makes Aa; reverse them and you get aA. Two a choices make aa. Each combination is equally likely. When A is dominant, meaning it shows whenever present, AA and both mixed pairs show that trait. Only aa shows the recessive trait, which appears when both alleles are a. So the letter pairs are one AA, two mixed, one aa: 1:2:1. The visible traits are 3:1. Two fair coin-like choices give those odds, not a guarantee for every four offspring.