Stnd 3 a CNotes Dihybrid Cross Punnett Square

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

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

How to use a Punnet Square to solve a dihybrid cross? 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? • Rr. Yy x Rr. Yy 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, r. Y, ry (parent 1) RY, Ry, r. Y, ry (parent 2)

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

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

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

Step 2: Give the genotypes of the parents. . . • Homozygous round green X wrinkled homozygous yellow plant • P 1 = WWgg X ww. GG

Step 3: Determine the Gametes. . . • WWgg X ww. GG WWgg = Wg, Wg, Wg ww. GG = w. G, w. G HINT: Foil to get the gametes

Step 4: Fill in the Punnett square. . . Wg Wg w. G Ww. Gg Ww. Gg

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

F 1 X F 1 = Rr. Yy X Rr. Yy • Remember to determine the gametes for your punnett square.

Fill in the Punnett Square WG Wg w. G wg WG WWGg Ww. GG Ww. Gg Wg WWGg WWgg Ww. Gg Wwgg w. G Ww. Gg ww. GG ww. Gg wg Ww. Gg Wwgg ww. Gg wwgg

The PATTERN. . . WG Wg w. G wg WG WWGg Ww. GG Ww. Gg Wg WWGg WWgg Ww. Gg Wwgg w. G Ww. Gg ww. GG ww. Gg Wg Ww. Gg Wwgg ww. Gg wwgg

What are the ratios? • Genotypic Ratio: – – – – – 1 WWGG 2 WWGg 1 WWgg 2 Ww. GG 4 Ww. Gg 2 Wwgg 1 ww. GG 2 ww. Gg 1 wwgg WG Wg w. G wg WG WWGg Ww. GG Ww. Gg Wg WWGg WWgg Ww. Gg Wwgg w. G Ww. Gg ww. GG ww. Gg Wg Ww. Gg Wwgg ww. Gg wwgg

Phenotypic Ratio: § Genotypic Ratio: § § § § § 1 WWGG 2 WWGg 1 WWgg 2 Ww. GG 4 Ww. Gg 2 Wwgg 1 ww. GG 2 ww. Gg 1 wwgg ** Explain the patterns G= yellow g = green W = round w = wrinkled • Phenotypic Ratio: – 9 Yellow Round • Dominant – 3 Yellow Wrinkled • Dominant Recessive – 3 Green Round • Recessive Dominant – 1 Green Wrinkled • Recessive

1. In rabbits, grey hair is dominant to white hair. Also in rabbits, black eyes are dominant to red eyes. GG = gray hair Gg = gray hair gg = white hair BB = black eyes Bb = black eyes bb = red eyes • What are the phenotypes (descriptions) of rabbits that have the following genotypes: – – Ggbb: gg. BB: Gg. Bb:

2. A male rabbit with the genotype GGbb is crossed with a female rabbit with the genotype gg. Bb 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? _____

3. A male rabbit with the genotype Gg. Bb is crossed with a female rabbit with the genotype Gg. Bb 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? _____

4. Show the cross between a gg. Bb 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? _____