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Dihybrid Crosses

Dihybrid Crosses. Biology 30 Mrs. S. Pipke-Painchaud. 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.

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Dihybrid Crosses

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  1. Dihybrid Crosses Biology 30 Mrs. S. Pipke-Painchaud

  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…. • G= yellow • g = green • W = round • w = wrinkled

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

  7. Step 3: Determine the Gametes . . . • WWgg X wwGG WWgg = Wg, Wg, Wg, Wg wwGG = wG, wG, wG, wG 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

  15. The Short Cut: • can only be used if you have • (Big little Big little X Big little Big little) • BbTt x BbTt • Do these fit? • BBTt X BbTt • BbTt x Bb tt

  16. Try this: C= Inflated Pod c = constricted pod D = Tall d = dwarf • The cross: a plant heterozygous for inflated pod and heterozygous tall is crossed with a another heterozygous inflated pod and heterozygous tall plant. What are the genotypic and phenotypic ratios? • The parents are: • CcDd x CcDd

  17. C= Inflated Pod c = constricted pod D = Tall d = dwarf Example: Genotypic Ratio: 1 2 1 2 4 2 1 2 1 Genotypic Ratio: 1 CCDD 2 CCDd 1 CCdd 2 CcDD 4 CcDd 2 Ccdd 1 ccDD 2 ccDd 1 ccdd • CcDd x CcDd • Does this fit the short cut? • Yes Phenotypic Ratio: (D) (D) 9 (D) ® 3 ® (D) 3 ® ® 1 Phenotypic Ratio: (D) (D) 9 Inflated Tall (D) ® 3 Inflated Dwarf ® (D) 3 Constricted Tall ® ® 1 Constricted Dwarf

  18. Now try . . . • Refer to the assigned questions in your duotang.

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