One gene one polypeptide theory can be explained by:-

Options

A. alkaptonuria
B. phenylketonuria
C. sickle cel anaemia
D. all of these

Answer

### Step-by-Step Solution:

1. **Understanding the One Gene One Polypeptide Theory**:
- The theory posits that each gene is responsible for the production of a single polypeptide chain, which can be part of a protein. This concept evolved from the earlier "one gene, one enzyme" hypothesis proposed by George Beadle.

2. **Historical Context**:
- In 1945, George Beadle proposed the idea that each gene corresponds to a specific enzyme. However, he later modified this to acknowledge that genes can also code for non-enzymatic proteins, leading to the broader "one gene, one polypeptide" theory.

3. **Examples of Genetic Disorders**:
- The theory can be illustrated through various genetic disorders:
- **Alkaptonuria**: Caused by a deficiency in the homogentisate dioxygenase (HGD) gene, leading to the accumulation of homogentisic acid, resulting in a disease state.
- **Phenylketonuria (PKU)**: This condition arises from a deficiency in the gene responsible for producing the enzyme phenylalanine hydroxylase. This enzyme is crucial for metabolizing the amino acid phenylalanine. Its accumulation can cause severe health issues.
- **Sickle Cell Anemia**: This genetic disorder is due to a mutation in the beta-globin gene, which alters the sixth amino acid in the polypeptide chain from glutamic acid to valine, affecting hemoglobin structure and function.

4. **Conclusion**:
- All three conditions (Alkaptonuria, Phenylketonuria, and Sickle Cell Anemia) exemplify the one gene one polypeptide theory, as they demonstrate how specific genes are linked to the production of particular polypeptides or proteins, and deficiencies or mutations in these genes lead to distinct diseases.