---
title: "Genetics Calculator — Punnett Square & Trait Probability"
description: "Build monohybrid and dihybrid Punnett squares. Model dominance, incomplete dominance, codominance, X-linked traits, and ABO blood types. Free for students."
url: "https://worldcalculators.org/calculators/genetics/"
canonical: "https://worldcalculators.org/calculators/genetics/"
---

# Genetics Calculator

Build monohybrid and dihybrid Punnett squares. Model dominance, incomplete dominance, codominance, X-linked traits, and ABO blood types. Free for students.

## Quick answer

Every Punnett square is a probability model. Mendel's law of segregation says the two alleles of a gene separate into different gametes, so a heterozygote (Aa) passes A or a to each child with 50% probability. His law of independent assortment says genes on different chromosomes are inherited independently — which is why the dihybrid 9:3:3:1 ratio is just two 3:1 ratios multiplied together.

## How geneticists use probability

Every Punnett square is a probability model. Mendel's law of segregation says the two alleles of a gene separate into different gametes, so a heterozygote (Aa) passes A or a to each child with 50% probability. His law of independent assortment says genes on different chromosomes are inherited independently — which is why the dihybrid 9:3:3:1 ratio is just two 3:1 ratios multiplied together.
The clean Mendelian ratios assume idealized conditions. Real inheritance often deviates:

## Frequently Asked Questions

A grid listing one parent's gametes along the top and the other's along the side. Each cell shows an offspring genotype, turning Mendelian segregation into countable probabilities — every cell is equally likely per child.
Genotype is the allele combination (AA, Aa, aa); phenotype is the observable trait. Under complete dominance, AA and Aa share a phenotype, so the 1:2:1 genotype ratio collapses to 3:1.

## Sources & Methodology

Punnett squares enumerate equally likely gamete combinations under Mendelian segregation and independent assortment; phenotype ratios follow from the selected dominance pattern (complete, incomplete, or codominant).

Source: https://worldcalculators.org/calculators/genetics/
Markdown mirror of the HTML page. Prefer this URL for RAG; the interactive calculator still lives on the HTML page.