Mendelian Ratio Calculator

Gregor Mendel's law of segregation states that each parent passes one of its two alleles to each offspring at random. For a single gene with a wild-type allele (+) and a mutant allele (m), crossing two heterozygous parents (+/m × +/m) yields offspring in the classic 1 : 2 : 1 ratio — 25 % wild-type (+/+), 50 % heterozygous (+/m), and 25 % homozygous mutant (m/m).

When you are working with multiple independent transgenes or knockout alleles, Mendel's law of independent assortment applies: genes on separate chromosomes are inherited independently, so the probability of any multi-gene combination is simply the product of the individual per-gene probabilities. A double homozygous knockout from two het × het crosses, for example, is expected in 1/4 × 1/4 = 1/16 (≈ 6.25 %) of offspring.

These ratios are population averages. Any individual litter can deviate substantially — especially with small litter sizes. Use the pups-to-genotype estimate to plan colony crosses that give you a statistically high chance of obtaining at least one animal with the target genotype.

1. Add one row per gene — click "Add gene" for each additional locus (up to 5). Give each gene a meaningful name so the results table is easy to read.
2. Set parent zygosities — choose wild-type (+/+), heterozygous (+/m), or homozygous (m/m) for each parent. The Punnett square is calculated instantly.
3. Choose the desired offspring zygosity — select the genotype you are trying to obtain for each gene. The calculator multiplies the per-gene probabilities to give the combined probability.
4. Enter your sample size — type how many pups you plan to genotype, or typically obtain per litter, to see how many matches to expect.
5. Set your confidence level — choose 90 %, 95 %, or 99 % to see how many pups you need to genotype to have that probability of obtaining at least one animal with the full target genotype.
6. Share or export — copy the URL to share your exact cross setup, or download a CSV for your lab notebook.