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Punnett Squares

Learn about Gregor Mendel's groundbreaking experiments investigating heredity in pea plants, his Punnett Squares method, and how traits are passed down through generations. Understand the outcomes of genetic crosses and the principles of dominance and recessiveness.

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Punnett Squares

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  1. Punnett Squares

  2. The Father of Genetics • Gregor Mendel performed the first major experiments investigating heredity. • Austrian Monk • Was college trained in Science and Math • Experimented between 1856-1863 • Investigated heredity in pea plants at his monastery.

  3. Mendel’s Experiments • Observed seven traits of pea plants: Plant height Pod Shape Flower Color Flower and Pod Position Seed Color Pod Color Seed Shape

  4. Crossing two plant traits • Using one trait at a time, Mendel crossed two plants who were true breeding for opposite forms of the same trait. Ex: Trait: Plant height Tall x Dwarf

  5. Punnett Square • A diagram that predicts the expected outcome of a genetic cross.

  6. Set up the Punnett Square • Write the genotypes of each parent. Put each allele (gene) in it’s own column. Then cross the alleles to determine the possible genotypes of the offspring Parent #1 Y Y y y Yy Yy Parent #2 Yy Yy

  7. Questions • How many of their offspring will be yellow? Hint: Each box is 25% 4 out of 4 – 100% (the dominant trait is stronger than the recessive trait) • How many of their offspring will be green? 0 • Are the offspring homozygous or heterozygous? heterozygous

  8. Example #2: Two plants that are heterozygous for seed color are crossed, what would their offspring look like? Yy Yy X Parent #1 Parent #2 Y y Y y YY Yy yy Yy

  9. Questions • What percent of the offspring are homozygous dominant? 1 out of 4 – 25% • What percent of the offspring are heterozygous? 2 out of 4 – 50% • What percentage of the offspring are homozygous recessive? 1 out of 4 – 25% • How many of offspring will be yellow? 75% • How many of the offspring will be green? 25%

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