Monohybrid cross sim
Choose the parent pea plants, drag their gametes and the genotypes into a Punnett square, then breed 4, 40 or 400 offspring and compare what you get with the expected ratio.
Monohybrid inheritance in pea plants: dominant and recessive alleles, homozygous and heterozygous, genotype and phenotype, gametes carrying one allele each, Punnett squares, the expected 3 : 1 and 1 : 1 ratios, and why small samples vary · covers the O-Level, IGCSE, GCSE topic
What the sim shows
Monohybrid cross in pea plants: one gene for stem height with two alleles, T (tall, dominant) and t (dwarf, recessive). Each parent has two alleles of the gene, one on each of a homologous pair of chromosomes (one from each of its own parents). Each gamete gets one allele of the pair. A Punnett square pairs each gamete of one parent with each gamete of the other: the four boxes are equally likely, so Tt × Tt is expected to give 1 TT : 2 Tt : 1 tt, which is 3 tall : 1 dwarf, and Tt × tt to give 1 tall : 1 dwarf. Each offspring is a separate chance, so a real batch only comes close to the expected ratio, and small batches vary a lot. Simplified on purpose: illustrative: a teaching model of pea plants, not real breeding data; one gene with two alleles, T (tall) and t (dwarf); complete dominance: a Tt plant is as tall as a TT plant; height depends only on the gene here; soil, light and water make no difference; seeded chance: a fixed list of random numbers, so the same steps always breed the same plants; each gamete is equally likely to carry either allele of the pair, and every seed grows; each parent is drawn with two gametes, one for each kind it can make; a real plant makes very many, half of each kind (a TT or tt plant makes only one kind); meiosis is shown only as each gamete getting one allele of the pair; for 4 and 40 plants each plant is drawn; for 400 each tile stands for up to 10 plants, one short stroke per plant; a batch of 4 shows each plant's genotype, which a real cross would not show: you see only its height; the chance spread is about two standard errors of the tall share (a normal approximation), so about 1 batch in 20 falls outside it by chance alone; below 20 plants it is too wide to judge; the plants are drawn smaller than real pea plants, and the bench models are teaching models.
- Glow: the part of the bench for the step you are on
- Close-up: the parents, their gametes, your Punnett square and the offspring you bred
- Dashed outline: an empty place to drop something
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