Punnett Squares Predicting the Probability of Inherited Traits

Probability: the likelihood that a particular event will occur Consider a coin flip: There are two possible outcomes (head or tails) The chance (or probability) of either outcome (heads or tails) is equal The probability that a single coin flip will be heads is 1 chance in 2 possibilities. 1/2 = 50% of flipping a heads or tails

Punnett Square: a tool to predict the probability of inheriting a specific trait. Mendel’s first generation cross: homozygous purple (PP) X purebred white (pp) 1. Draw a box: 2. Mom’s alleles --> P P 3. Dad’s alleles --> p p 4. Fill in the boxes 5. Offspring genotype- 100% Pp 6. Offspring phenotype - 100% purple Pp

Heterozygous (Pp) X Heterozygous (Pp) P p P p X PP Pp pp Offspring Genotypes: 1 PP: 2Pp: 1pp Offspring Phenotypes: 3 Purple: 1 White Genotypic Ratio: The probability of having each Genotype. 1:2:1 = 25% chance of PP, 50% chance of Pp, 25% pp Phenotypic Ratio: The probability of having each phenotype. 3:1= 75% chance of being purple, 25% chance of being white