To solve the question regarding the dihybrid test cross ratio, we can follow these steps:
### Step 1: Understand Dihybrid Cross
A dihybrid cross involves two traits, where each trait is represented by two alleles. For example, consider two traits: seed shape (round vs. wrinkled) and seed color (yellow vs. green).
**Hint:** Remember that a dihybrid cross involves two different traits, each with two alleles.
### Step 2: Define Hybrid Organism
A hybrid organism is heterozygous for the traits being studied, meaning it has two different alleles for each trait. For instance, if we denote round seeds as 'R' and wrinkled seeds as 'r', and yellow seeds as 'Y' and green seeds as 'y', a dihybrid organism could be RrYy.
**Hint:** A hybrid organism has different alleles for the traits being crossed.
### Step 3: Conduct the Test Cross
In a dihybrid test cross, the dihybrid organism (RrYy) is crossed with a homozygous recessive organism (rryy). This means we are crossing RrYy (heterozygous for both traits) with rryy (homozygous recessive for both traits).
**Hint:** A test cross involves crossing a hybrid with a homozygous recessive organism.
### Step 4: Determine the Gametes
The gametes produced by the dihybrid organism (RrYy) will be RY, Ry, rY, and ry. The homozygous recessive organism (rryy) can only produce one type of gamete: ry.
**Hint:** Identify the gametes produced by both parents to set up the cross.
### Step 5: Set Up the Punnett Square
Using a Punnett square, we can determine the offspring from the cross. The rows will represent the gametes from the dihybrid parent (RrYy), and the columns will represent the gametes from the homozygous recessive parent (rryy).
**Hint:** A Punnett square helps visualize the combinations of alleles from the parents.
### Step 6: Analyze the Offspring
When we fill out the Punnett square, we will find the following combinations:
- RrYy (Round, Yellow)
- Rryy (Round, Green)
- rrYy (Wrinkled, Yellow)
- rryy (Wrinkled, Green)
This results in four different phenotypes, each appearing in a 1:1:1:1 ratio.
**Hint:** Count the phenotypes to determine the ratio.
### Step 7: Conclusion
The phenotypic ratio of the offspring from a dihybrid test cross is 1:1:1:1.
**Final Answer:** The dihybrid test cross ratio is 1:1:1:1.
