Trihybrid Cross Calculator

A trihybrid cross studies inheritance of THREE different traits simultaneously. Parents differ at three gene loci (e.g., A/a, B/b, C/c). This creates complex genotypes: AABBCC × aabbcc produces F1 hybrids all heterozygous (AaBbCc). Selfing F1 produces 64 possible combinations in F2 (2⁶ = 64.genotypes), following 27:9:9:9:3:3:3:1 phenotypic ratio when genes assort independently (as in Mendelian dihybrid, but extended to three traits).

For trihybrid cross (AaBbCc × AaBbCc): Expected ratios are 27:9:9:9:3:3:3:1 for all dominant/recessive. Each trait independently follows 3:1 ratio (AA:Aa:aa). Combining: (3:1)³ = 27:9:9:9:3:3:3:1. For complete dominance, phenotypes are: 27 all dominant, 9 with two dominant traits, 9 with two dominant, 9 (actually three categories for each two-trait combo), 3 single dominant, etc. For three independent traits, 8 phenotypic classes exist with the ratios shown.

Each gene pair (loci) segregates independently during meiosis (Mendel's Second Law). Each parent produces 8 gamete types (2³ = 8) representing all combinations: ABC, ABc, AbC, Abc, aBC, aBc, abC, abc. These combine randomly during fertilization. Independent assortment requires: genes on different chromosomes OR far apart on same chromosome (no linkage). Linkage (genes on same chromosome close together) violates independent assortment - linked genes show 3:1 ratios nearer 1:1.

Trihybrid analysis determines: whether genes are linked, map distances between genes on chromosomes, epistasis (gene interactions), and confirms Mendel's laws. Linkage mapping uses recombination frequency: 1% recombination = 1 centiMorgan (cM). F2 data from trihybrid shows if expected 27:9:9:9:3:3:3:1 ratio deviates - indicating linkage or epistasis. Human traits are nearly all polygenic (many genes) - trihybrid is basic model for complex trait genetics. Crop breeding: stack beneficial alleles across multiple genes.