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Pick a cross and choose the parents' genotypes. The tool draws the genetic diagram and the Punnett square and works out the ratios. Pick your exam board to see what your specification asks for. Then read a family tree, try the chi-squared calculator, the quiz and the exam questions.
Every ratio below is worked out by the same tool, from two parents that are heterozygous for every gene (a test cross where the cross says so). Use it to revise, or print this page.