Genotype & Phenotype Ratio Calculator

Type any two parent genotypes — Aa, AaBb, AaBbCc and beyond — and get the simplified genotypic and phenotypic ratios instantly. Handles monohybrid, dihybrid, trihybrid and tetrahybrid crosses.

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Genotypic vs phenotypic ratio

The genotypic ratio counts exact allele pairs (e.g. 1 AA : 2 Aa : 1 aa). The phenotypic ratio counts what you can see (e.g. 3 dominant : 1 recessive).

They differ because a heterozygote (Aa) usually looks identical to a homozygous dominant (AA).

The classic ratios

  • Monohybrid Aa×Aa → 3:1 (geno 1:2:1)
  • Dihybrid AaBb×AaBb → 9:3:3:1
  • Trihybrid AaBbCc×AaBbCc → 27:9:9:9:3:3:3:1
  • Test cross Aa×aa → 1:1

How to enter a genotype

  • Write each gene as a letter pair: Aa, BB, cc.
  • Chain genes together: AaBbCc.
  • Upper case = dominant, lower case = recessive.
  • Both parents must use the same gene letters (up to 4 genes).

How the math works

Each parent's gametes are every combination of one allele per gene (2n gametes). The tool combines all gamete pairs, groups offspring by genotype and by phenotype, then divides by the greatest common divisor for the simplest whole-number ratio.

Why it beats counting by hand

A trihybrid cross has 64 boxes and a tetrahybrid 256 — far too many to draw reliably. This calculator computes the exact ratios in a fraction of a second, with no Punnett-square arithmetic errors.

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