Learning Target: Traits and Probability I Can…Create a Punnett square predicting possible geno- and phenotypes of offspring and analyze the results I Will… Determine potential gametes of parents Complete a Punnett square of the cross Analyze the geno- and phenotype ratio and percentage for the offspring Ch. 6.5 pp

Now that we know about how the parents donate their genetic traits to their offspring, let’s predict the offspring characteristics: R.C. Punnett developed a method to keep track of the various possible genetic combinations of offspring Punnett square: grid system for predicting all possible genotypes from a cross (mating of two parents) Axes – potential gametes Boxes – possible offspring Punnett square: grid system for predicting all possible genotypes from a cross (mating of two parents) Axes – potential gametes Boxes – possible offspring

Parent gamete Possible Offspring Possible Offspring Punnett square Haploid Diploid

Punnett square steps: 1.Determine parents’ genotype for desired trait and write the cross. Cross: Bb x bb Trait: Eye color Dominant: Brown color (B) Recessive: Blue (b) Parent PhenotypeGenotype DescriptionSymbol Heterozygous Bb Homozygous Recessivebb ♂ Brown eyes ♀ Blue eyes

Punnett square steps: 2. Split parents’ genotype to represent their gametes and fill-in the axes of the Punnett square. b bb b b B Bb

Punnett square steps: 3. Place the alleles into the offspring boxes Drop the top axis letters down the column into each box below it Bring the side axis letters across to each box in the same row Each box should have two letters in it b b b B B B b bb b b b Customary to write the Dominant letter first within the box

Punnett square steps: 4. Analyze the possible offspring: Write down all the genotype combinations B bb B b b Offspring Genotype Combination PercentageGenotype Description Trait Phenotype Eye color Bb 2/4 = 50%HeterozygousBrown bb 2/4 = 50%Homozygous recessive Blue 2Bb :2bb= 1:1 ratio

Probability – predicts the likelihood of a particular genotype or phenotype occurring. Probability = Number of ways a specific event can occur Number of total outcomes Common Probabilities – Monohybrid Homozygous dominant x Homozygous recessive Genotype – 100% Heterozygous Phenotype 100% dominant Heterozygous x Heterozygous Genotype – 1:2:1 Phenotype 25% Homozygous dominant, 50% Heterozygous, 25% Homozygous recessive Homozygous dominant x Heterozygous Genotype – 1:1 Phenotype – 50% Homozygous dominant, 50% heterozygous Homozygous recessive x Heterozygous Genotype – 1:1 Phenotype – 50% Heterozygous, 50% Homozygous recessive Common Probabilities – Monohybrid Homozygous dominant x Homozygous recessive Genotype – 100% Heterozygous Phenotype 100% dominant Heterozygous x Heterozygous Genotype – 1:2:1 Phenotype 25% Homozygous dominant, 50% Heterozygous, 25% Homozygous recessive Homozygous dominant x Heterozygous Genotype – 1:1 Phenotype – 50% Homozygous dominant, 50% heterozygous Homozygous recessive x Heterozygous Genotype – 1:1 Phenotype – 50% Heterozygous, 50% Homozygous recessive

Learning Check √: Traits and Probability Create and complete a Punnett square of the following cross for eye color: Homozygous Brown x Homozygous blue Key: Dominant: Brown (B) Recessive: Blue (b) What are the chances of having a blue-eyed offspring?