Origin of short-legged Ancon sheep variety occurs by ..................

Explanation

**Step-by-Step Text Solution:**

1. **Understanding the Ancon Sheep**: The Ancon sheep is a variety known for its short legs. This variety originated due to a specific genetic change.

2. **Identifying the Cause**: The origin of the short-legged Ancon sheep is attributed to a mutation. Mutations are sudden changes in the genetic material that can lead to new traits.

3. **Type of Mutation**: The mutation that led to the Ancon sheep is classified as a recessive mutation. This means that the trait for short legs is not expressed unless an individual has two copies of the mutated gene.

...