Punnett Squares
Punnett squares predict offspring genotypes.
About this topic
A Punnett square is a grid for predicting the genotypes and phenotypes of offspring from a cross. Put one parent's gametes along the top and the other's down the side, then fill each box by combining the alleles. A monohybrid cross of two heterozygotes (Aa × Aa) gives a 1 AA : 2 Aa : 1 aa genotype ratio and a 3 : 1 phenotype ratio.
Dihybrid crosses use a 4 × 4 grid and give 9:3:3:1. Results are probabilities, not guarantees.
Cross two heterozygous brown-eyed parents, Bb x Bb. The grid gives BB, Bb, Bb and bb, so the genotype ratio is 1:2:1 and the phenotype ratio is 3 brown to 1 blue, meaning each child has a 25 percent chance of blue eyes. A test cross with a homozygous recessive partner reveals whether a dominant-looking individual is BB or Bb.
Breeders and genetic counsellors use Punnett squares to estimate probabilities. Remember these are chances, not guarantees: having three brown-eyed children does not make the next one more likely to be blue, because each birth is independent. Students commonly mix up genotype, the allele combination, with phenotype, the observable trait. Always write out the parents' gametes first.
Key ideas
- Each parent contributes one allele
- Tt × Tt gives 3:1 phenotypes
- Probabilities multiply
Quick check
Use cases: where Punnett Squares helps
- Homework: review the key idea behind Punnett Squares before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Punnett Squares without notes.
- Visual learning: play with the interactive lab to see how Punnett Squares changes when you adjust its inputs.
- Teaching a friend: explain Punnett Squares in your own words, then compare your version with the key ideas.
Biology underpins medicine, farming, conservation and biotechnology.
Frequently asked questions
What is Punnett Squares?
Punnett squares predict offspring genotypes.
What will I learn in Punnett Squares?
Each parent contributes one allele. Tt × Tt gives 3:1 phenotypes. Probabilities multiply.
Is Punnett Squares part of Biology?
Yes. It is one of 150 Biology topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Punnett Squares lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Punnett Squares?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.