Dihybrid Crosses

Dihybrid Crosses Biology

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

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

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?

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

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

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

Step 4: Fill in the Punnett square . . .

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

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

Fill in the Punnett Square Do you see a pattern?

The PATTERN . . .

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

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

Dihybrid Crosses