An interactive Punnett Square calculator to work out patterns of inheritance for a recessive genetic disease, such as cystic fibrosis.

What is the chance a child will have a recessive genetic disease? Drag an icon from the top for the mother and father, representing the gene combinations that determine straight or peaked hairline. Tap MATE and see all possible gene combinations for offspring based on the parents’ genes. A recessive disease results when offspring inherit two copies of a recessive gene (d) – one from each parent. In this case, 1 of 4 possible gene combinations is dd, so 25% of offspring will have the disease. Dd offspring (50%) have one dominant and one recessive gene; they will not have the disease but are “carriers” of the recessive gene. A DD offspring does not have the disease. There is no possibility of passing on a recessive gene (d) to the next generation. A Dd offspring does not have the disease, but is a “healthy carrier” with one copy of the recessive gene (d) that may be passed on to the next generation. A dd offspring has the disease, and will pass the recessive gene (d) on to the next generation. Tap OFFSPRING again to see which of the four possible gene combinations may occur for another pregnancy.

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