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C-Notes: Dihybrid Cross (Punnett Square w/ 2 traits)

C-Notes: Dihybrid Cross (Punnett Square w/ 2 traits). Stnd : 3a. 01/22/14. SWBAT: predict possible outcomes of phenotypes in a genetic cross with two traits from the genotypes. Objective:. Studying the inheritance of one trait Ex: Yy x YY Studying the inheritance of Two traits

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C-Notes: Dihybrid Cross (Punnett Square w/ 2 traits)

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  1. C-Notes: Dihybrid Cross (Punnett Square w/ 2 traits) Stnd: 3a 01/22/14 SWBAT: predict possible outcomes of phenotypes in a genetic cross with two traits from the genotypes. Objective:

  2. Studying the inheritance of one trait • Ex: Yy x YY • Studying the inheritance of Two traits • A dihybrid cross can be treated as two separate monohybrid crosses. • This proves his Theoryon the “Law of Independent Assortment”(two traits are inherited INDEPENDENTLY) • Trait 1: Round/wrinkled (texture) • Trait 2: yellow/green (color) • Ex: RrYy x RrYy What is a Monohybrid cross? What is a Dihybrid Cross?

  3. Step 1: Determine the parental genotypes • Ex: A pea plant that is heterozygous for round, yellow seeds is self fertilized, what are the phenotypic ratios of the resulting offspring? • RrYy x RrYy Step 2: Determine the gametes. This might feel like a FOIL method you learned in math. Combine the R’s and Y’s of each parent to represent sperm and egg. Do this for both parents. x Gametes after foil “FOIL” RY, Ry, rY, ry (parent 1) RY, Ry, rY, ry(parent 2) How to use a Punnet Square to solve a dihybrid cross?

  4. RY Ry rY ry RY Ry rY ry Step 3: set up a large 4x4 punnet square, place one gamete set from the parent on the top, and the other on the side. 

  5. Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 9:3:3:1 phenotypic ratio Step 4: Write the genotypes of the offspring in each box and determine how many of each phenotype you have.

  6. 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?

  7. Step 1: Make a Key…. • G= yellow • g = green • W = round • w = wrinkled

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

  9. Step 3: Determine the Gametes . . . • WWgg X wwGG WWgg = Wg, Wg, Wg, Wg wwGG = wG, wG, wG, wG HINT: Foil to get the gametes

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

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

  12. F1 X F1 = RrYyX RrYy • Remember to determine the gametes for your punnett square. RrYyX RrYy

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

  14. The PATTERN . . .

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

  16. 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

  17. 1. In rabbits, grey hair is dominant to white hair. Also in rabbits, black eyes are dominant to red eyes. • What are the phenotypes (descriptions) of rabbits that have the following genotypes: • Ggbb: • Ggbb: • ggBB: • GgBb:

  18. 2. A male rabbit with the genotype GGbb is crossed with a female rabbit with the genotype ggBb The square is set up below. Fill it out and determine the phenotypes and proportions in the offspring. How many out of 16 have grey fur and black eyes? ____ How many out of 16 have grey fur and red eyes? _____ How many out of 16 have white fur and black eyes? ____ How many out of 16 have white fur and red eyes? _____

  19. 3. A male rabbit with the genotype GgBb is crossed with a female rabbit with the genotype GgBb The square is set up below. Fill it out and determine the phenotypes and proportions in the offspring. How many out of 16 have grey fur and black eyes? ____ How many out of 16 have grey fur and red eyes? _____ How many out of 16 have white fur and black eyes? ____ How many out of 16 have white fur and red eyes? _____

  20. 4. Show the cross between a ggBb and a GGBb. You'll have to set the square up yourself! How many out of 16 have grey fur and black eyes? ____ How many out of 16 have grey fur and red eyes? _____ How many out of 16 have white fur and black eyes? ____ How many out of 16 have white fur and red eyes? _____

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