Punnett Square
Calculate monohybrid cross Punnett square genotype and phenotype ratios for one trait with two alleles. Free online genetics calculator with Punnett square grid, charts, and probability breakdowns.
Mother's Genotype
Father's Genotype
About This Calculator
The Punnett Square Calculator is a genetics tool that predicts the possible genotypes and phenotypes of offspring from a cross between two parents for a single trait (monohybrid cross). Named after Reginald Punnett, this diagram is essential for students learning Mendelian genetics, biology researchers analyzing inheritance patterns, and anyone studying how traits are passed from one generation to the next.
The calculator uses Mendelian inheritance principles to compute all possible allele combinations. A — the dominant allele — masks the recessive allele a in heterozygous (Aa) individuals. The 2x2 Punnett square grid shows every possible genotype combination (AA, Aa, aa), and the calculator automatically computes the genotypic ratio (e.g., 1:2:1) and phenotypic ratio (e.g., 3:1). Results include detailed frequency breakdowns and interactive charts for both genotypes and phenotypes.
How to Use
Select the mother's and father's genotypes from the dropdown menus. Each parent can be homozygous dominant (AA), heterozygous (Aa), or homozygous recessive (aa). Click Calculate to generate the Punnett square and view the predicted offspring distribution. The results section shows the Punnett square grid, genotype and phenotype counts and percentages, and the simplified ratios.
Regional Notes
Mendelian genetics and Punnett squares are universal concepts taught in biology curricula worldwide. This calculator follows standard Mendel's laws — the Law of Segregation and the Law of Independent Assortment — which apply equally in India (CBSE/ICSE curriculum), the United States (NGSS standards), the United Kingdom (GCSE/A-Level biology), and across all educational systems. The allele notation (A = dominant, a = recessive) follows international genetics conventions.
Frequently Asked Questions
What is a Punnett square and how does it work?
A Punnett square is a diagram used in genetics to predict the possible genotypes of offspring from a cross between two parents. It works by listing the alleles of one parent across the top and the alleles of the other parent down the side, then combining them in each cell to show all possible genotype combinations. For a monohybrid cross (one trait), the 2x2 grid shows the four possible allele combinations from the parents.
What is the difference between genotype and phenotype?
Genotype refers to the genetic makeup of an organism — the specific combination of alleles (e.g., AA, Aa, or aa). Phenotype refers to the observable physical traits that result from the genotype. For example, if A (dominant) codes for brown eyes and a (recessive) codes for blue eyes, both AA and Aa genotypes result in the brown eye phenotype, while only aa results in blue eyes.
What does a genotypic ratio of 1:2:1 mean?
A 1:2:1 genotypic ratio means that out of four possible offspring combinations, one will be homozygous dominant (AA), two will be heterozygous (Aa), and one will be homozygous recessive (aa). This is the classic ratio seen when both parents are heterozygous (Aa x Aa) for a single trait following Mendelian inheritance.
What does a phenotypic ratio of 3:1 mean?
A 3:1 phenotypic ratio means that three out of four offspring will display the dominant trait and one will display the recessive trait. This occurs when both parents are heterozygous (Aa x Aa) for a single trait. Three offspring inherit at least one dominant allele (AA or Aa) and show the dominant phenotype, while one inherits two recessive alleles (aa) and shows the recessive phenotype.
How do I determine if a parent is homozygous or heterozygous?
A homozygous parent has two identical alleles for a trait — either both dominant (AA) or both recessive (aa). A heterozygous parent has one dominant and one recessive allele (Aa). When a parent is homozygous dominant (AA), all offspring will inherit a dominant allele. When homozygous recessive (aa), all offspring inherit a recessive allele. A heterozygous parent (Aa) passes the dominant allele 50% of the time and the recessive allele 50% of the time.
What is the difference between monohybrid and dihybrid Punnett squares?
A monohybrid Punnett square tracks one trait (two alleles) and produces a 2x2 grid with 4 possible combinations. A dihybrid Punnett square tracks two traits (four alleles) and produces a 4x4 grid with 16 possible combinations. Monohybrid crosses show simple 3:1 phenotypic ratios, while dihybrid crosses show 9:3:3:1 ratios when both parents are heterozygous for both traits.
Is this Punnett square calculator free to use?
Yes, this Punnett square calculator is completely free to use with no registration required. All features including the Punnett square grid, genotype and phenotype frequency charts, and ratio calculations are available at no cost.
Can I share my Punnett square results?
Yes, the calculator saves your parent genotype selections in the URL, so you can copy and share the link to share your specific Punnett square results with classmates, teachers, or study groups.