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

What is a Monohybrid cross? What is a Dihybrid Cross? 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 Theory on the “Law of Independent Assortment” ( two traits are inherited INDEPENDENTLY) – Trait 1: Round/wrinkled (texture) – Trait 2: yellow/green (color) Ex: RrYy x RrYy

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? 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)

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.RYRyrYry RYRy rY ry 

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.

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 P1 = WWgg X wwGG

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

Step 4: Fill in the Punnett square... WgWgWgWg wGWwGgWwGgWwGgWwGg wGWwGgWwGgWwGgWwGg wGWwGgWwGgWwGgWwGg wGWwGgWwGgWwGgWwGg

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 = RrYy X RrYy Remember to determine the gametes for your punnett square.

Fill in the Punnett SquareWGWgwGwgWGWWGGWWGgWwGGWwGg WgWWGgWWggWwGgWwgg wGWwGGWwGgwwGGwwGg wgWwGgWwggwwGgwwgg

The PATTERN... WGWgwGwg WG WWGG WWGg WwGG WwGg Wg WWGg WWgg WwGg Wwgg wG WwGG WwGg wwGG wwGg Wg WwGg Wwgg wwGg wwgg

What are the ratios? Genotypic Ratio: – 1 WWGG – 2 WWGg – 1 WWgg – 2 WwGG – 4 WwGg – 2 Wwgg – 1 wwGG – 2 wwGg – 1 wwgg WGWgwGwg WGWWGGWWGgWwGGWwGg WgWWGgWWggWwGgWwgg wGWwGGWwGgwwGGwwGg WgWwGgWwggwwGgwwgg

Phenotypic Ratio: – 9 Yellow Round Dominant Dominant Dominant Dominant – 3 Yellow Wrinkled Dominant Recessive Dominant Recessive – 3 Green Round Recessive Dominant Recessive Dominant – 1 Green Wrinkled Recessive Recessive Recessive Recessive  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 ** Explain the patterns

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: GG = gray hair Gg = gray hair gg = white hair BB = black eyes Bb = black eyes bb = red eyes

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? _____ 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.

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? _____

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? _____