Punnett square calculator: what it does
A punnett square calculator predicts the distribution of offspring outcomes for a Mendelian cross by enumerating parental gametes (allele combinations produced by meiosis) and combining them in a grid. The outputs are typically reported as genotype ratios, phenotype ratios, and probabilities.
Working assumption used here: a monohybrid cross is shown using one gene with two alleles written as two letters (for example, Aa). Uppercase represents the dominant allele; lowercase represents the recessive allele.
How the calculation works (conceptual steps)
- List gametes for each parent. For Aa, gametes are A and a, each with probability \(0.5\).
- Fill the grid. Each cell combines one gamete from Parent 1 and one from Parent 2 to form an offspring genotype.
- Compute probabilities. Each cell probability is \(P(\text{cell}) = P(\text{gamete}_1)\cdot P(\text{gamete}_2)\).
- Count outcomes. Summing cell probabilities by genotype and by phenotype yields genotype and phenotype ratios.
Interpreting ratios produced by a punnett square calculator
For a standard monohybrid cross, the Punnett square has four cells. When both parents are heterozygous (Aa × Aa), each gamete is produced with probability \(0.5\), so each cell has probability \(0.5\cdot 0.5 = 0.25\). Counting outcomes yields the familiar results:
Genotype ratio (Aa × Aa): \(1\,AA : 2\,Aa : 1\,aa\)
Phenotype ratio (A dominant): \(3\) dominant : \(1\) recessive
Extension to multiple genes (why dihybrid grids are larger)
If a parent is heterozygous at \(n\) independently assorting genes, the number of distinct gamete types is \(2^n\). A full Punnett grid for two such parents contains \(2^n \times 2^n = 4^n\) genotype combinations (for example, \(n=2\) gives a \(4 \times 4\) grid with \(16\) cells).