Punnett Square Generator

The genotype ratio counts the exact allele combinations in the offspring -- for an Aa x Aa cross, that's 1 AA : 2 Aa : 1 aa. The phenotype ratio groups AA and Aa together because they look identical under complete dominance, giving 3 dominant-looking offspring for every 1 recessive-looking offspring (3:1). Two genotypically different individuals (AA and Aa) can be phenotypically indistinguishable, which is exactly what a test cross (crossing with an aa individual) is used to reveal.

When both parents are AA, every gamete from both parents carries only the A allele, so every offspring must be AA -- there's no other genetic combination possible. The same logic applies to aa x aa (all aa offspring). Punnett squares only produce a probability spread when at least one parent is heterozygous (Aa), because that's the only genotype that produces two different types of gametes.

No -- those are polygenic traits controlled by many genes plus environmental factors, producing a continuous range of outcomes rather than a few discrete categories. A monohybrid Punnett square only models a single gene with two alleles and complete dominance, so it's appropriate for traits like pea seed shape or certain single-gene human conditions, not for multi-gene or continuously varying traits.

This calculator assumes complete dominance, where the heterozygote looks identical to the homozygous dominant parent. Codominant traits (like AB blood type, where both alleles are expressed) and incomplete dominant traits (like a red x white cross producing pink) follow different phenotype rules that this simple dominant/recessive model does not represent -- the genotype ratio math would still apply, but the phenotype grouping would need to be reworked for those inheritance patterns.