Monohybrid Cross Calculator
Calculate the expected offspring ratios for a single-trait Mendelian genetic cross.
Enter parent genotypes to see phenotype and genotype probabilities.
What Is a Monohybrid Cross? A monohybrid cross examines the inheritance of a single trait between two parents. Gregor Mendel established the principles of heredity in the 1860s using pea plants, observing how traits like seed color and plant height were passed to offspring.
Genotype Notation
- A = dominant allele (capital letter)
- a = recessive allele (lowercase letter)
- AA = homozygous dominant — expresses dominant trait
- Aa = heterozygous — expresses dominant trait (carrier)
- aa = homozygous recessive — expresses recessive trait
The Punnett Square Method List one parent’s alleles across the top, the other’s down the side. Fill in each box by combining one allele from each parent. Count the resulting genotypes to find the expected ratio.
Example: Aa × Aa (both carriers) Cross result: 1 AA : 2 Aa : 1 aa Phenotype: 3 dominant : 1 recessive (the classic 3:1 ratio) This means 75% of offspring express the dominant trait, 25% express the recessive trait.
Important Note These ratios represent probability, not certainty. Each individual offspring is an independent event — like a coin flip. Actual offspring may not perfectly match the predicted ratio, especially in small litters.