Score: 0
Growing Season
Time: 150
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About Punnett Pen

Breed plants with hidden genotypes, fill real Punnett squares and run test crosses to fulfill phenotype contracts in this free online Mendelian genetics game.

Punnett Pen is a free online Punnett square game where you run a breeding farm under contract. Every plant in your pen displays a visible phenotype but hides its genotype, so filling orders for purple flowers or true-breeding wrinkled seeds forces you to think like Gregor Mendel: breed, count the offspring and reason backward from the ratios.

Every cross in this genetics game is computed by real Mendelian rules. Parents make gametes carrying one allele per gene, the Punnett board maps every fertilization and offspring arrive at the predicted 3:1 and 1:2:1 ratios. Recessive phenotypes always prove a homozygous genotype, while dominant plants stay ambiguous until you run a test cross against a known homozygous recessive tester. Later contracts introduce incomplete dominance where heterozygotes show a third phenotype, dihybrid crosses with the classic 9:3:3:1 split, sex-linked traits where carrier mothers hide alleles from sons and lethal alleles that bend the 3:1 ratio into a 2:1.

This is the same reasoning geneticists use for pedigree analysis, carrier screening and crop and animal breeding. Mendel derived the laws of segregation and independent assortment from pea ratios alone, and every modern genotyping lab still verifies suspected carriers with controlled crosses.

Key Science Concepts

What You'll Learn

Grade Level: Middle School, High School

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How to play

  1. Read Contracts Contract cards demand phenotypes or proven genotypes. Each has a deadline counted in crosses.
  2. Pick Two Parents Tap two adult plants in the pen, then hit BREED. Phenotypes are visible but genotypes stay hidden.
  3. Watch the Square The Punnett board fills by real probability. Offspring seeds drop into the tray to plant or deliver.
  4. Deliver & Infer Tap a contract then a plant or seed to deliver. Use test crosses against the pp tester to prove genotypes.
  5. Mind the Season Every cross drains water. Tap the season gauge for a greenhouse boost with a short cooldown.
  6. New Genes Arrive Contracts escalate through incomplete dominance, dihybrids, sex-linkage and lethal alleles.

Frequently asked questions

Is Punnett Pen free to play?
Yes. Punnett Pen is completely free to play in your browser. There is no download, install or account needed.
What grade level is Punnett Pen for?
Punnett Pen is designed for Middle School, High School students and works well as a classroom activity or homework.
Does Punnett Pen work on phones and tablets?
Yes. Punnett Pen runs in any modern browser on desktop computers, Chromebooks, tablets and phones in landscape mode.

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