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## How to Approach a Dihybrid Cross Let's use pea seeds this time - they're easier to fit in a Punnett square. | Flower color | Flower position | Seed color | Seed shape | Pod shape | Pod color | Stem length | |---|---|---|---|---|---|---| | Purple | Axial | Yellow | Round | Inflated | Green | Tal...

## How to Approach a Dihybrid Cross Let's use pea seeds this time - they're easier to fit in a Punnett square. | Flower color | Flower position | Seed color | Seed shape | Pod shape | Pod color | Stem length | |---|---|---|---|---|---|---| | Purple | Axial | Yellow | Round | Inflated | Green | Tall | | White | Terminal | Green | Wrinkled | Constricted | Yellow | Dwarf | ## Dihybrid Crosses 1. **P Generation** - RRYY x rryy 2. **F1 Generation** - RrYy x RrYy 3. **F2 Generation Test Cross** - RrYy x rryy not needed as we have our answer ### 2. **F1 Generation** - RrYy x RrYy (Dihybrid heterozygous lines) | | RY | ry | Ry | ry | |---|---|---|---|---| | RY | RRYY | RrYY | RRYy | RrYy | | ry | RrYY | rrYY | RrYy | rrYy | | Ry | RrYy | RrYy | RRyy | Rryy | | ry | RrYy | rrYy | Rryy | rryy | **Offspring:** All round All yellow ### 9:3:3:1 | | RY | ry | Ry | ry | |---|---|---|---|---| | RY | RRYY | RrYY | RRYy | RrYy | | ry | RrYY | rrYY | RrYy | rrYy | | Ry | RrYy | RrYy | RRyy | Rryy | | ry | RrYy | rrYy | Rryy | rryy | - **Round Yellow** - **Wrinkled Yellow** - **Round Green** - **Wrinkled Green** ## Mono Hybrid Heterozygous Cross (eg. Aa x Aa): Genotype ratio = 1:2:1 Phenotype ratio = 3:1 ## Dihybrid Heterozygote Cross (eg. AaBb x AaBb): Genotype ratio = 1:2:2:1:4:1:2:2:1 Phenotype ratio = 9:3:3:1 Q. Does a pea have to be yellow to be round? ## Mendel's 3rd Law: Principle of Independent Assortment Allele pairs separate independently during formation of gametes (meiosis). | | **AB** | **Ab** | **aB** | **ab**| |---|---|---|---|---| | **AB** | AABB | AABb | AaBB | AaBb | | **Ab** | AABb | AAbb | AaBb | Aabb | | **aB** | AaBB | AaBb | aaBB | aaBb | | **ab** | AaBb | Aabb | aaBb | aabb |