Calculadora de Cruzamento Triíbrido
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
AaBbCc × AaBbCc → 27:9:9:9:3:3:3:1; P(A_B_C_) = (3/4)³
About this calculator
The Trihybrid Cross Calculator is an educational tool for genetics students and professionals. It calculates the expected phenotypic ratios from a cross between two individuals heterozygous for three independent genes (AaBbCc × AaBbCc). The result is the well-known ratio 27:9:9:9:3:3:3:1, representing the eight possible phenotypic classes. The calculator also provides the probability of an offspring showing the dominant phenotype for all three genes, which is (3/4)³ or 27/64.
The calculation is based on the independent assortment of alleles and the product rule. For each gene, the probability of an offspring inheriting the dominant allele from both parents is 3/4. Since the genes are independent, the joint probability is the product of the individual probabilities. The calculator applies this principle to generate the frequencies of each genotypic and phenotypic combination, displaying the results clearly.
This tool is useful in educational settings, such as Mendelian genetics classes, and for exam preparation like college entrance exams. It can also assist researchers working with crosses involving multiple genes, allowing quick verification of expected ratios. However, the 27:9:9:9:3:3:3:1 ratio is only valid if the genes are on different chromosomes and there is no linkage.
Cautions: the calculator assumes independent genes and no interactions such as epistasis or incomplete dominance. In cases of linked genes, the ratios may differ. Also, environmental factors that affect phenotypic expression are not considered. Always verify that conditions of genetic independence are met before using the results.
Frequently asked questions
What does the ratio 27:9:9:9:3:3:3:1 mean?
This ratio represents the expected phenotypic proportions in a trihybrid cross. 27 corresponds to the dominant phenotype for all three genes (A_B_C_), the three 9s represent phenotypes with two dominant and one recessive (e.g., A_B_cc), the three 3s represent phenotypes with one dominant and two recessive (e.g., A_bbcc), and the 1 is the recessive phenotype for all genes (aabbcc).
How to calculate the probability of an offspring being heterozygous for all genes?
The probability of being heterozygous for one gene (Aa) is 1/2. For three independent genes, the joint probability is (1/2)³ = 1/8. The calculator does not provide this directly, but you can calculate it manually.
Does the calculator work for crosses with linked genes?
No. The calculator assumes independent assortment, i.e., genes on different chromosomes. If genes are linked, the phenotypic ratios will differ and depend on the distance between them. In that case, use a linkage calculator.
Can I use the calculator for crosses with incomplete dominance?
No. The calculator assumes complete dominance, where the dominant allele masks the recessive. For incomplete dominance, the phenotypic ratios are different (e.g., 1:2:1 for one gene). The tool does not cover these cases.
What is the difference between trihybrid and triibrido?
They are synonyms. 'Trihybrid' is the English term, and 'triibrido' is a Portuguese variant. The calculator works for both terms.