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Dihybrid Crosses

Dihybrid crosses analyze the inheritance of two characteristics simultaneously, exemplified by Mendel's study of round yellow versus wrinkled green seeds. This approach demonstrates the Law of Independent Assortment, where traits segregate independently during gamete formation. By following systematic steps, including determining parent genotypes, gametes, and filling in a Punnett square, students can uncover phenotypic and genotypic ratios. For example, crossing homozygous round green and wrinkled homozygous yellow plants yields specific ratios, revealing the inheritance patterns of traits.

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Dihybrid Crosses

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  1. Dihybrid Crosses Biology

  2. Dihybrid Crosses • the natural progression for Mendel was to study 2 characteristics at the same time. • thus, the study of 2 pairs of contrasting traits at the same time = a dihybrid cross • ex.. round yellow seeds X wrinkled green seeds

  3. Mendel’s Fourth Law • The Law of Independent Assortment • During gamete formation, segregating pairs of unit factors assort independently of each other. • the two traits are inherited totally independently of each other. • i.e. color is inherited independently of seed shape. • Example: • Homozygous round green X wrinkled homozygous yellow

  4. Solving Dihybrid Crosses • Follow the steps • If you were to cross a Homozygous round green X wrinkled homozygous yellow plant, what would your phenotypic and genotypic ratios be?

  5. Step 1: Make a Key…. • Y= yellow • y = green • R = round • r = wrinkled

  6. Step 2: Give the genotypes of the parents. . . • Homozygous round green X wrinkled homozygous yellow plant • P1 = RRyy X rrYY

  7. Step 3: Determine the Gametes . . . • RRyy X rrYY RRyy = Ry, Ry, Ry, Ry rrYY = rY, rY, rY, rY HINT: Foil to get the gametes

  8. Step 4: Fill in the Punnett square . . .

  9. Step 5: Answer any questions . . . • Genotypic ratio • = all WwGg • Phenotypic ratio • = all round yellow G= yellow g = green W = round w = wrinkled

  10. F1 X F1 = WwGg X WwGg • Remember to determine the gametes for your punnett square. WwGg X WwGg

  11. Fill in the Punnett Square Do you see a pattern?

  12. The PATTERN . . .

  13. What are the ratios? • Genotypic Ratio: • 1 WWGG • 2 WWGg • 1 WWgg • 2 WwGG • 4 WwGg • 2 Wwgg • 1 wwGG • 2 wwGg • 1 wwgg

  14. G= yellow g = green W = round w = wrinkled Phenotypic Ratio: • Genotypic Ratio: • 1 WWGG • 2 WWGg • 1 WWgg • 2 WwGG • 4 WwGg • 2 Wwgg • 1 wwGG • 2 wwGg • 1 wwgg • Phenotypic Ratio: • 9 Yellow Round • Dominant Dominant • 3 Yellow Wrinkled • Dominant Recessive • 3 Green Round • Recessive Dominant • 1 Green Wrinkled • Recessive Recessive ** Explain the patterns

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