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Punnett Squares

This article explores the pioneering work of Gregor Mendel, the Father of Genetics, who conducted groundbreaking experiments on heredity between 1856 and 1863 using pea plants. It delves into his observations of seven traits and how he utilized Punnett Squares to predict genetic outcomes from plant crosses. Learn how to set up Punnett Squares, interpret genotypes, and answer key genetic questions as we illustrate Mendel's significant contributions to our understanding of inheritance and the principles of dominant and recessive traits.

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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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