BRAINCAKEProbability
Genetic ratios are really probabilities. A probability is a number from 0 (impossible) to 1 (certain), and can be written as a fraction, decimal or percentage. A 3 : 1 ratio means each offspring has a probability of ¾ of the dominant phenotype and ¼ of the recessive phenotype.
Each fertilisation is an independent event. The outcome for one child does not affect the next. If a couple have an affected child, the chance that the next child is affected is exactly the same.
Two rules let you combine probabilities.
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