Ace the OnRamps Biology Challenge 2026 – Dive into Your Future with Science!

With complete dominance, having one dominant allele is enough to display the dominant trait. When two heterozygotes (one dominant and one recessive allele each) mate, the offspring genotypes appear in a 1:2:1 ratio (AA, Aa, Aa, aa). Because both AA and Aa show the dominant phenotype, while only aa shows the recessive phenotype, the expected phenotypes appear in a 3:1 ratio: three with the dominant trait for every one with the recessive trait. The other patterns described come from either the genotypic ratio or different crosses, so the 3:1 dominant to recessive phenotype is the correct result.