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Probability and Punnett Squares. Probability. Probability a number that describes how likely it is something will happen Can be expressed as a ratio, fraction, or percentage When you flip a coin, you have what probability of getting heads? 1 out of 2 1 : 2 (ratio) ½ (fraction)
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Probability • Probability a number that describes how likely it is something will happen • Can be expressed as a ratio, fraction, or percentage • When you flip a coin, you have what probability of getting heads? • 1 out of 2 • 1 : 2 (ratio) • ½ (fraction) • 50% (percentage)
Punnett Squares • Chart that shows all the possible outcomes of a genetic cross – allows you to determine the probability
Determining genotype and phenotype ratios from a punnett square • Genotype Ratios • 1 GG : 2 Gg : 1 gg • 25% GG, 50% Gg, 25% gg • Phenotype Ratios • 3 Green : 1 white • 75% Green, 25% white
Practice!!! • In chickens, brown feathers are dominant to blue. • Cross a heterozygous brown chicken with a blue chicken. Give genotype and phenotype ratios Genotypes : 50 % Bb , 50 % bb Phenotypes: 50% Brown, 50 % blue