Biology Calculator
Punnett Square Calculator
Easily generate accurate Punnett squares for monohybrid (one-trait) or dihybrid (two-trait) genetic crosses. Calculate the exact genotype and phenotype probability percentages, frequencies, and ratios for offspring based on parent alleles.
Punnett Square Calculator
Calculate genotype and phenotype probabilities
Trait 1
Results
Enter parent genotypes to generate square
How to Use the Punnett Square Calculator
A Punnett Square is an essential biological tool used to predict the genetic variations and probabilities of offspring from a specific breeding event. To get accurate results, follow these steps:
- Select the Cross Type: Choose between a Monohybrid (1 trait) or Dihybrid (2 traits) cross.
- Choose Dominance (Monohybrid Only): For a single trait, you can select Complete Dominance, Incomplete Dominance (traits blend), or Codominance (both traits express).
- Input Parent Genotypes: Ensure you use the exact uppercase and lowercase combinations (e.g.,
AaorAaBb) for both parents. - Review the Results: The tool will output the visual grid, listing all possibilities and aggregating them into easy-to-read genotypic and phenotypic ratios.
Calculating Probabilities
In a monohybrid cross, there are 4 total outcomes (2×2 grid). In a dihybrid cross, there are 16 total outcomes (4×4 grid). The genotypic ratio represents the distribution of actual allele combinations, while the phenotypic ratio represents the distribution of expressed physical traits.
Example Crosses
Example 1 — Monohybrid Cross (Heterozygous)
Trait: Seed Shape, Parent 1: Rr, Parent 2: Rr
Total Combinations: 4
Genotypes: RR (1/4 or 25%), Rr (2/4 or 50%), rr (1/4 or 25%)
Genotypic Ratio: 1:2:1
Phenotypes (Complete Dominance): Round (75%), Wrinkled (25%)
Phenotypic Ratio: 3:1
Example 2 — Incomplete Dominance
Trait: Flower Color, Parent 1: Rr, Parent 2: rr
Dominance: Incomplete (Blended Traits)
Total Combinations: 4
Genotypes: Rr (50%), rr (50%)
Phenotypes: Pink (Blended) 50%, White 50%
Genotypic & Phenotypic Ratio: 1:1
Example 3 — Dihybrid Cross
Traits: Seed Shape (R/r) & Color (Y/y). Parents: RrYy × RrYy
Total Combinations: 16 (4x4 Grid)
Gametes per Parent: RY, Ry, rY, ry
Phenotypic Breakdown:
- 9/16 Round, Yellow (R_Y_)
- 3/16 Round, Green (R_yy)
- 3/16 Wrinkled, Yellow (rrY_)
- 1/16 Wrinkled, Green (rryy)
Phenotypic Ratio: 9:3:3:1
Understanding the 9:3:3:1 Ratio
In genetics, a 9:3:3:1 ratio is a classic outcome of a dihybrid cross between two organisms that are heterozygous for two different traits (e.g., AaBb × AaBb). It means 9 offspring show both dominant traits, 3 show the first dominant and second recessive trait, 3 show the first recessive and second dominant trait, and 1 shows both recessive traits.
Frequently Asked Questions
- What is a Punnett Square?
- A Punnett square is a visual representation used in genetics to predict the possible genotypes and phenotypes of an offspring from a specific cross or breeding experiment. It displays all possible combinations of maternal and paternal alleles.
- What is the difference between a genotype and a phenotype?
- A genotype is the genetic makeup of an organism, represented by alleles (e.g., RR, Rr, or rr). A phenotype is the observable physical characteristic or trait resulting from that genotype (e.g., Round or Wrinkled seeds).
- What are dominant and recessive alleles?
- Dominant alleles (typically written in uppercase, like R) express their trait even if only one copy is present (Rr). Recessive alleles (lowercase, like r) require two copies to be expressed (rr).
- What is the difference between Complete Dominance, Incomplete Dominance, and Codominance?
- In Complete Dominance, the dominant allele completely masks the recessive one (e.g., Red + White = Red). In Incomplete Dominance, the traits blend (e.g., Red + White = Pink). In Codominance, both traits are expressed simultaneously without blending (e.g., Red + White = Red and White spotted).
- What is a dihybrid cross?
- A dihybrid cross predicts the inheritance of two different traits simultaneously (e.g., seed shape and seed color). It results in a 4x4 grid with 16 possible allele combinations, often yielding a classic 9:3:3:1 phenotypic ratio when both parents are heterozygous (RrYy).