Which out of these is an example of Pleiotropism:

Options

A. Human skin colour.
B. Phenylketonuria.
C. Inheritance of flower colour in Snapdragon.
D. ABO blood grouping in humans.

Explanation

To solve the question regarding which of the given options is an example of pleiotropism, we need to understand the concept of pleiotropy.

### Step-by-Step Solution:

1. **Understanding Pleiotropism**:
- Pleiotropism refers to the phenomenon where a single gene influences multiple phenotypic traits. This means that one gene can have several effects on an organism's characteristics.

2. **Analyzing the Options**:
- **Option 1: Human Skin Color**:
- Human skin color is influenced by multiple genes (polygenic inheritance) rather than a single gene, so this is not an example of pleiotropism.
- **Option 2: Phenylketonuria (PKU)**:
- PKU is caused by a mutation in a single gene that affects the metabolism of phenylalanine. This mutation leads to multiple symptoms, including mental retardation and changes in skin and hair pigmentation. Thus, this is a clear example of pleiotropism.
- **Option 3: Inheritance of Flower Color in Snapdragons**:
- This trait is typically an example of incomplete dominance and involves multiple alleles, but it does not illustrate pleiotropism as it does not show multiple phenotypic effects from a single gene.
- **Option 4: ABO Blood Grouping in Humans**:
- ABO blood grouping is determined by multiple alleles at a single locus, but it does not demonstrate pleiotropism since it does not affect multiple traits.

3. **Conclusion**:
- After analyzing all the options, the correct answer is **Option 2: Phenylketonuria (PKU)**, as it is a condition caused by a mutation in a single gene that results in multiple phenotypic effects.

### Final Answer:
The example of pleiotropism is **Phenylketonuria (PKU)**.

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