In shorthorn cattle genes for red `(r_1)` and white `(r_2)` coat colour occur. Crosses between red `(r_1 r_1)` and white `(r_2 r_2)` produced `(r_1 r_2)` roan. This is an example of

Options

A. Complementary genes
B. Epistasis
C. Codominance
D. Incomplete dominance

Explanation

To solve the question regarding the coat color inheritance in shorthorn cattle, we need to analyze the genetic cross and the resulting phenotypes. Here’s a step-by-step breakdown:

### Step 1: Identify the Alleles
In shorthorn cattle, the genes for coat color are represented as:
- Red coat color: \( r_1 \) (homozygous dominant: \( r_1 r_1 \))
- White coat color: \( r_2 \) (homozygous recessive: \( r_2 r_2 \))

**Hint:** Identify the alleles involved in the genetic cross.

### Step 2: Understand the Cross
When red cattle (\( r_1 r_1 \)) are crossed with white cattle (\( r_2 r_2 \)), the offspring produced are heterozygous (\( r_1 r_2 \)).

**Hint:** Consider what happens when two homozygous individuals are crossed.

### Step 3: Determine the Offspring Phenotype
The offspring (\( r_1 r_2 \)) exhibit a roan phenotype, which is a mix of red and white. This indicates that both alleles are expressed in the phenotype.

**Hint:** Look at the resulting phenotype from the cross and how it relates to the parent phenotypes.

### Step 4: Classify the Inheritance Pattern
In this case, both alleles \( r_1 \) and \( r_2 \) are expressed equally in the roan offspring. This is characteristic of co-dominance, where both traits are fully expressed.

**Hint:** Review the definitions of co-dominance, incomplete dominance, and other genetic concepts to find the correct classification.

### Step 5: Conclusion
Since both the red and white colors are expressed in the roan offspring, this example illustrates co-dominance.

**Final Answer:** The correct answer is co-dominance.