Free tool
Enter two parent genotypes for one gene (Aa x Aa) or two genes (AaBb x AaBb) to get each parent's gametes, the full Punnett square, and the genotype and phenotype ratios with percentages.
Built for General Biology and AP Biology geneticsUse one letter per gene, capital for the dominant allele: Aa, BB, AaBb. Both parents need the same genes. Assumes complete dominance and independent assortment.
Enter two genotypes to see the Punnett square.
Punnett squares get easy once gametes and ratios are automatic. Encodr keeps genetics like this on a spaced-repetition schedule so it holds until the exam.
Get started freeEach parent makes gametes that carry one allele of each gene (Mendel's law of segregation). With two genes on different chromosomes, the alleles sort into gametes independently of each other (the law of independent assortment), so an AaBb parent makes four gamete types in equal numbers: AB, Ab, aB and ab. Write one parent's gametes across the top and the other's down the side. Each box is one equally likely offspring genotype.
Monohybrid example: Aa x Aa gives 1 AA : 2 Aa : 1 aa, a 1:2:1 genotype ratio. With complete dominance AA and Aa look the same, so the phenotype ratio is 3 dominant : 1 recessive (75% and 25%).
Dihybrid example: AaBb x AaBb gives a 4 x 4 square of 16 boxes and a 9:3:3:1 phenotype ratio: 9/16 show both dominant traits, 3/16 and 3/16 show one recessive trait each, and 1/16 is aabb. The same answer comes from the product rule: 3/4 x 3/4 = 9/16 for both dominant traits.
Test cross: crossing a dominant-looking individual with a homozygous recessive (aa) reveals its genotype. An AA parent gives all dominant offspring; an Aa parent gives a 1:1 ratio.
In the phenotype column, A_ means at least one dominant A allele (AA or Aa). The ratios assume complete dominance and unlinked genes. Incomplete dominance, codominance, epistasis and linked genes change the phenotype ratio. See the General Biology I flashcards for those cases.
How to set up a Punnett square, get genotype and phenotype ratios, run a test cross, and skip the 16-box grid with the product rule.
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