Solve AaBbCc crosses without drawing a 64-box grid. This calculator builds parent gametes, combines them, and reports exact genotype and phenotype probabilities for three independently assorting genes.
Use Basic mode for the answer. Open Advanced mode when you need gamete frequencies, expected counts, genotype classes, and a downloadable table.
Enter three allele pairs for each parent. The calculator builds gametes, combines them, and reports exact phenotype and genotype probabilities.
Example: AaBbCc means one heterozygous locus for each of A, B, and C.
Normalized: AaBbCc
Example: aabbcc is the triple-recessive tester used in a trihybrid test cross.
Normalized: AaBbCc
Selected result
Probability: 42.19%
Expected count from 640 offspring: 270
Most likely class
42.19%
This class has the largest probability under the current genotype model.
abc
12.50%
abC
12.50%
aBc
12.50%
aBC
12.50%
Abc
12.50%
AbC
12.50%
ABc
12.50%
ABC
12.50%
abc
12.50%
abC
12.50%
aBc
12.50%
aBC
12.50%
Abc
12.50%
AbC
12.50%
ABc
12.50%
ABC
12.50%
A standard AaBbCc × AaBbCc cross gives the phenotype ratio 27:9:9:9:3:3:3:1 when all three genes assort independently and each dominant allele masks its recessive partner. The most common class is A_B_C_ at 27/64, or 42.19%. The rarest class is aabbcc at 1/64, or 1.56%.
The fast method multiplies single-gene probabilities. For A_B_C_, use 3/4 × 3/4 × 3/4. For aabbcc, use 1/4 × 1/4 × 1/4. This is the same logic used by the forked-line method, but the calculator also handles custom parent genotypes.
Each heterozygous locus gives a parent two possible alleles in gametes. AaBbCc has three heterozygous loci, so it makes 2³ = 8 gamete types. Two parents with eight gamete types each create 8 × 8 = 64 fertilisation combinations.
Mendel’s law of independent assortment states that alleles at different genes sort into gametes independently when those genes are unlinked. OpenStax explains independent assortment through dihybrid crosses, and the same probability rule extends to three loci. Nature Education also describes independent assortment as the separation of different genes during gamete formation.
Real data can depart from this model. Linked loci, epistasis, reduced viability, incomplete dominance, and small sample size can change offspring ratios. If your observed class counts deviate from 27:9:9:9:3:3:3:1, test the numbers with a Mendelian ratio chi-square calculator before changing your genetic model.
Sources: OpenStax Biology 2e and Nature Education.
The tool separates inputs, genetic assumptions, and outputs so students can see each step instead of copying a final ratio.
Each single-gene heterozygote cross gives a 3/4 chance of the dominant phenotype. Multiply the three independent probabilities: 3/4 × 3/4 × 3/4 = 27/64. The answer is 42.19%.
If the class counted 640 offspring, the expected number of A_B_C_ offspring equals 640 × 27/64 = 270. This count gives a clear target for lab data.
The heterozygous parent makes eight gamete types. The triple-recessive parent makes only abc gametes. Each heterozygote gamete therefore creates one matching offspring class.
If the genes assort independently, each phenotype appears at 1/8, or 12.5%. Large excesses of parental classes can point toward linkage, so compare this result with a genetic linkage calculator when your data show unequal test-cross classes.
Genes close together on the same chromosome produce too many parental gametes.
One gene can mask or modify another gene, so 27:9:9:9:3:3:3:1 no longer applies.
Rare classes such as aabbcc can disappear by chance when offspring numbers stay low.
Similar phenotypes can make counts drift away from the expected classes.
Multiply single-gene probabilities without drawing a large Punnett square.
Solve two-trait crosses before moving to three-trait inheritance problems.
Compare observed trihybrid offspring counts with expected Mendelian ratios.
A trihybrid cross tracks three genes at the same time. A standard example uses AaBbCc × AaBbCc. Each heterozygous parent can make eight gamete types, so the cross has 64 possible zygote combinations before identical classes merge. The calculator uses segregation and independent assortment to calculate each genotype and phenotype probability.
The classic complete-dominance ratio is 27:9:9:9:3:3:3:1. The largest class, A_B_C_, appears in 27 of 64 expected offspring. The triple-recessive class, aabbcc, appears in 1 of 64 expected offspring. This ratio assumes independent assortment and no epistasis, linkage, viability bias, or scoring error.
A parent that is heterozygous at all three loci makes eight gamete types. The formula is 2ⁿ, where n equals the number of heterozygous loci. AaBbCc produces ABc, AbC, Abc, aBC, aBc, abC, abc, and ABC at equal frequency. A parent with a homozygous locus makes fewer gamete types because that locus contributes only one allele.
A 64-box grid works, but it wastes time and hides the pattern. Probability multiplication gives the same answer faster. For example, the chance of A_B_C_ in AaBbCc × AaBbCc equals 3/4 × 3/4 × 3/4 = 27/64. This method scales better when you move from two traits to three traits.
Yes. Enter AaBbCc for one parent and aabbcc for the tester parent. If all three genes assort independently, the eight phenotype classes each appear at 12.5%. Strong departures from that pattern can suggest linkage, selection, small sample noise, or phenotype scoring problems.
No. This calculator assumes that the three loci assort independently. Linked genes do not follow the standard trihybrid ratios because parental gametes appear more often than recombinant gametes. Use a linkage-specific calculator when loci sit close together on the same chromosome.
Yes. Use three matched allele pairs, such as RrYyTt or AaBbCc. Each pair must contain the same gene letter in uppercase and lowercase form. The calculator treats uppercase letters as dominant alleles and lowercase letters as recessive alleles for phenotype grouping.