crosscalc

Monohybrid cross calculator

One gene, two parents, a 2×2 Punnett square. Choose each parent’s genotype to see the offspring genotypes, phenotypes and their probabilities.

♀ Mother
♂ Father
Quick set:
Name your traits (optional)
A/a
Phenotype ratio
Genotype ratio
Cross
cross×calc

Phenotype ratio Genotype ratio Combinations

Phenotypes

Gametes

Punnett square

Columns are the mother's (♀) gametes, rows the father's (♂). Cells are coloured by phenotype.

Genotypes

Made with crosscalc.com ·

The three monohybrid crosses to know

CrossGenotypesPhenotypes
AA × aaall Aaall dominant
Aa × Aa1 AA : 2 Aa : 1 aa3 : 1
Aa × aa1 Aa : 1 aa1 : 1

Moving on to two genes? The dihybrid cross calculator extends this to a 4×4 square. For how the two compare, read monohybrid vs dihybrid crosses.

FAQ

What ratio does Aa × Aa give?

A 3:1 phenotype ratio (three dominant-looking to one recessive) and a 1:2:1 genotype ratio (AA : Aa : aa).

What does Aa × aa give?

A 1:1 ratio — half the offspring are Aa and show the dominant trait, half are aa and show the recessive one. This is the monohybrid test cross.

Can two dominant-looking parents have a recessive child?

Yes, if both are heterozygous (Aa). Each passes on the recessive allele with probability ½, so there is a ¼ chance of an aa offspring.