Generate Punnett squares for monohybrid (2×2) and dihybrid (4×4) crosses. Color-coded grids, phenotype ratio bars, genotype breakdown tables, inheritance pattern detection, and common cross presets.
The Punnett square is the most fundamental tool in Mendelian genetics. Developed by Reginald Punnett in the early 1900s, it provides a visual way to predict the probability of offspring inheriting particular genotypes from two parents. Each parent contributes one allele per gene, and the Punnett square systematically maps every possible combination.
This calculator generates a complete Punnett square for a monohybrid cross — one gene with two alleles. Enter each parent's genotype (e.g., Aa × Aa) and instantly see the 2×2 grid, offspring genotype ratios, and phenotype probabilities. Whether you are studying dominant versus recessive traits, working through a biology assignment, or predicting outcomes in plant or animal breeding, this tool gives you instant, error-free results.
Understanding Punnett squares is essential for genetics students, breeders, genetic counselors, and anyone curious about how traits are inherited. Dominant alleles (capital letters) mask recessive alleles (lowercase letters), creating predictable ratios that Mendel first documented with pea plants over 150 years ago.
Drawing Punnett squares by hand is straightforward for a single cross but becomes tedious and error-prone for multiple traits or when checking many crosses quickly. This calculator automatically determines every possible offspring combination, computes exact ratios, and identifies dominant vs. recessive phenotypes — all instantly. It is perfect for verifying homework, exploring different parent combinations, and understanding inheritance patterns.
Monohybrid Cross (one gene, two alleles): Each parent contributes one allele. Parent 1 alleles: [a₁, a₂] Parent 2 alleles: [b₁, b₂] Offspring combinations: a₁b₁, a₁b₂, a₂b₁, a₂b₂ Probability of each genotype = (count of that genotype) / 4 Classic Aa × Aa cross: AA : Aa : aa = 1 : 2 : 1 Dominant : Recessive = 3 : 1
Result: AA: 25%, Aa: 50%, aa: 25%
When two heterozygous parents (Aa) are crossed, the Punnett square produces AA, Aa, aA, and aa. Combining Aa and aA (both heterozygous), the genotype ratio is 1 AA : 2 Aa : 1 aa. The phenotype ratio is 3 dominant : 1 recessive (75% show the dominant trait, 25% show the recessive trait).
Reginald Punnett, a British geneticist, created the Punnett square around 1905 while working with William Bateson to extend Mendel's work. It became the standard teaching tool for genetics because it makes probability calculations visual and intuitive. Gregor Mendel had derived the underlying laws decades earlier using thousands of pea plant crosses, but Punnett's grid made the math accessible.
While the basic Punnett square assumes complete dominance, real genetics features incomplete dominance (red × white = pink flowers), codominance (AB blood type), multiple alleles (blood type has three: A, B, O), and epistasis (one gene affecting another). However, the Punnett square framework still applies — you just need to account for different dominance relationships when interpreting the phenotype column.
Punnett squares are used in genetic counseling to estimate the risk of inherited conditions, in agriculture and animal breeding to plan crosses for desirable traits, and in forensics and paternity analysis. Understanding them is essential for any biology or life sciences course.
A Punnett square is a grid used in genetics to predict the genotypes of offspring from a cross between two parents. Each row represents an allele from one parent, and each column represents an allele from the other. The cells show all possible offspring genotypes and their expected ratios.
Genotype is the genetic makeup — the specific alleles an organism carries (e.g., Aa). Phenotype is the observable trait expressed by those alleles (e.g., brown eyes). Dominant alleles can mask recessive ones, so different genotypes (AA and Aa) can produce the same phenotype.
Heterozygous means an organism has two different alleles for a gene (e.g., Aa). Homozygous means it has two identical alleles — either homozygous dominant (AA) or homozygous recessive (aa). Heterozygous individuals carry both versions of the gene.
Yes! Switch to Dihybrid mode to analyze two genes simultaneously (e.g., AaBb × AaBb). This generates a 4×4 grid with 16 offspring combinations and shows the classic 9:3:3:1 phenotype ratio for independent assortment.
When two Aa parents are crossed, the four offspring possibilities are AA, Aa, aA, and aa. Three of these (AA, Aa, aA) carry at least one dominant allele and show the dominant phenotype, while only one (aa) is homozygous recessive. Hence the 3:1 ratio. This only applies to the specific Aa × Aa cross.
A test cross breeds an organism showing the dominant phenotype with a homozygous recessive individual (aa). If any offspring show the recessive phenotype, the dominant parent must be heterozygous (Aa). If all offspring are dominant, the parent is likely homozygous dominant (AA).