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PATTERNS OF HEREDITY CAN BE PREDICTED • PUNNETT SQUARES SHOW POSSIBLE OUTCOMES FOR INHERITANCE • RATIOS AND PERCENTAGES CAN EXPRESS THE PROBABLITY OF OUTCOMES. PUNNETT SQUARE • Shows how the parent’s alleles might combine in offspring • Top of square shows one parent’s alleles for a trait (D,D for dominant tall); while side shows other parent’s alleles for the trait (d,d for recessive short) • Each box shows way the alleles from each parent would combine in offspring. (In this case, each child would be Dd, one dominant and one recessive, so they would all be tall. Ratios can Express Probability • RATIO: compares the relationship between 2 quantities. 4:4 is four out of four • PROBABILITY: the chance of a specific outcome in relation to the total number of possible outcomes. Percentages can Express Probability • PERCENTAGE: is a ratio that compares a number to 100. (the chance 2 hybrid black guinea pigs Bb, will have a recessive brown pig bb, is 25% or 25 out of 100. Punnett square shows it as 1:4. • Punnett squares & probability do not guarantee the outcome, only predict an outcome. Calculating Probability • Human females have 2 X-chromosomes (X,X) & males are (X,y). The punnett square shows only 2 possible outcomes (male-Xy or female-XX). • Punnett squares & probability only predict the likelihood of different outcomes, the actual experimental results may not match predicted outcomes.