Understanding Dihybrid Crosses
Dihybrid crosses study two traits at the same time. They help learners predict how alleles may pass from parents to offspring. A classic example uses seed shape and seed color. Each parent makes gametes that carry one allele for each trait. When gametes meet, the offspring genotype is formed.
Independent Assortment
This calculator follows Mendelian independent assortment. It works best when the two genes assort independently, and each trait has a clear dominant allele. A heterozygous parent such as AaBb can make four gamete types. These are AB, Ab, aB, and ab. The square then combines each gamete from parent one with each gamete from parent two.
Genotype and Phenotype
The genotype ratio shows the exact allele pairs found in the offspring grid. It may include groups such as AABB, AaBb, or aabb. The phenotype ratio groups offspring by visible trait outcomes. With complete dominance, any uppercase allele gives the dominant trait. Two lowercase alleles give the recessive trait.
Classic Ratio
A standard AaBb by AaBb cross gives a 9:3:3:1 phenotype ratio. Nine offspring show both dominant traits. Three show the first dominant trait and second recessive trait. Three show the first recessive trait and second dominant trait. One shows both recessive traits. This pattern changes when parents are homozygous, mixed, or test crossed.
Practical Use
Use the tool for homework checks, classroom demonstrations, breeding examples, and quick lesson planning. Enter two allele pairs for each parent. Keep each pair in a two-character format, such as Aa, aa, BB, or Bb. Use uppercase letters for dominant alleles. Use lowercase letters for recessive alleles.
Probability Notes
The table is a probability model, not a guarantee. Real offspring counts can differ because fertilization is random. Larger sample sizes usually move closer to the expected ratio. Smaller families can look very different from the square.
Test Cross Value
Teachers can also show why test crosses matter. A parent with a dominant phenotype may hide a recessive allele. Crossing that parent with a double recessive partner can reveal the hidden genotype. This makes the square a strong bridge between math and observable biology.
Exporting Results
The downloadable files help save your work. CSV output is useful for spreadsheets. PDF output is useful for reports and worksheets. Always compare the result with the biological assumptions behind your cross.