Notes – Punnett Squares

Vocabulary Terms Phenotype = physical appearance of a trait Example: purple flowers Genotype = the combination of alleles that an individual has for a particular gene Example: PP or Pp or pp

Vocabulary Terms Homozygous = having two of the same alleles Example: PP or pp Heterozygous = having two different alleles Example: Pp

Punnett squares predict the offspring genotypes Use these steps: Determine the genotypes of parents Determine the alleles in the gametes Combine gametes: bring over and down Analyze the results Phenotype ratio Genotype ratio Pp P p PP Pp pp 3 purple : 1 white 1PP : 2Pp : 1pp

Oral Practice: What are the phenotypes of the parents? What are the genotypes of the parents? What are the genotypes and phenotypes of the offspring in the top row? What are the genotypes and phenotypes of the offspring in the bottom row? Pair-share: one student answers the odds and the other answers the evens.

Practice #1 In peas, the gene for tall (T) is dominant to the gene for short (t). Predict the offspring genotype and phenotype ratios if a plant that is heterozygous tall is crossed with a plant that is short? Reminder: Follow the steps in your notes to create a Punnett square.