Punnett Square Calculator
Predict the genotype and phenotype ratios of offspring from any genetic cross. Enter parent genotypes to see inheritance probabilities.
Use uppercase for dominant allele, lowercase for recessive (e.g., B = black, b = white)
Enter the second parent's genotype
Name your trait for clearer results
How does a Punnett square work?
A Punnett square diagrams all possible combinations of parental alleles to predict offspring genotypes. For each parent, gametes carry one allele from each gene pair. The square shows every pairing: rows represent one parent's gametes, columns represent the other parent's. Each cell shows the offspring genotype from combining those two alleles. Dominant alleles (uppercase) mask recessive alleles (lowercase) in heterozygous individuals.
What is the difference between genotype and phenotype?
Genotype is the genetic makeup - the alleles inherited (e.g., AA, Aa, aa). Phenotype is the physical trait expressed - what you can observe (e.g., black fur vs. white fur). A dominant allele (uppercase) shows its phenotype even with one copy (Aa = black), while recessive (lowercase) only shows when homozygous (aa = white). This is why genotypic ratios often differ from phenotypic ratios.
What do the ratios mean?
Genotypic ratio shows expected frequency of each genotype (e.g., 1:2:1 for AA:Aa:aa). Phenotypic ratio shows visible trait distribution (e.g., 3:1 for dominant:recessive). The ratios are probabilities - with more offspring, actual results approach expected ratios. For multiple loci, ratios multiply: dihybrid cross gives 9:3:3:1 phenotypic ratio.
Why does my cross show only one genotype?
This means both parents are homozygous (e.g., AA × aa = all Aa). All offspring are heterozygous and show the dominant phenotype but carry the recessive allele. This is called a "carrier" situation - important in breeding programs where hidden recessive traits could reappear in later generations if carriers bred together.