Using the Punnett Square Marcellin Biology Notes

Using the Punnett Square The Punnett Square is used to show the possible combinations of traits that may appear in the children. Every trait is based on probability. Probability = chance

Using the Punnett Square: More Genetic Vocabulary Genotype- a person’s genes Shown by letters (ex. BB, Bb, bb) Phenotype- a person’s physical appearance (Ex. Brown eyes, blue eyes)

Using the Punnett Square The basic Punnett Square looks like a window pane.

Using the Punnett Square 1. Determine the genotype of the 2 parents. 2. Write down your “cross” (mating). (ex. Tt x tt) 3. Draw a Punnett square.

Step #4: "Split" the letters of the genotype for each parent & put them "outside" the p-square.  For an example cross we'll use these parental genotypes: Tt x tt.  Take the genotype letters of one parent, split them and put them on the left, outside the rows of the p-square. Using the Punnett Square 4. Split the letters of the genotype for each parent & put them on the outside of the Punnett Square. Now take the two letters of the second parent's genotype, split them up, and place them above each of the two columns of the p-square.

Using the Punnett Square 5. Determine the possible genotypes of the children by filling in the Punnett square. Filling in the top-left box: Filling in the bottom- left box: Filling in the top-right box: Filling in the bottom- right box: Filling in the top-left box: Filling in the bottom- left box: Filling in the top-right box: Filling in the bottom- right box: Tt tt??

Using the Punnett Square 6. Summarize the results. Genotypes: Tt, tt Probability: ½ Tt, ½ tt If we determined that T= tall and t = short, what would the phenotypes be? Tall and short What would the probabilities be? ½ Tall, ½ short