What does a Punnett square show?

Every way the gametes from two parents can meet. Each square is one possible offspring, so the genotype and phenotype ratios can be read straight off the grid.

What is the ratio from a cross of two hybrid (Pp) parents?

Three purple to one white in phenotype (3 : 1), and 1 PP to 2 Pp to 1 pp in genotype (1 : 2 : 1).

What is the ratio from a dihybrid cross RrYy × RrYy?

9 : 3 : 3 : 1 in phenotype, because the two genes assort independently.

Why do sons get X-linked traits more often than daughters?

Sons have one X chromosome and no second copy to mask a recessive allele, so one recessive allele shows. Daughters need two.

What is incomplete dominance?

Neither allele is fully dominant. A red (RR) and white (WW) parent give all pink (RW) offspring, and two pinks give red, pink and white in a 1 : 2 : 1 ratio.

Did Mendel really get 3 : 1?

Yes, to within chance: his F₂ counts for flower colour were 705 purple to 224 white. The simulation shows how the ratio settles as more peas are counted.

🧬 Biology · The science of living things

Punnett Square

Cross two parents, drag alleles into the grid and see the offspring ratios.

Punnett square

Ready to explore

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Phenotype ratio—

Chance of selected—

Gametes placed—

Observed sample—