Tumour-causing virus has:

Options

A. t-onc genes
B. c-onc genes
C. v-onc genes
D. tv-onc genes

Explanation

**Step-by-Step Solution:**

1. **Understanding Tumors**: A tumor is a mass of tissue that forms when cells grow and divide more than they should. Normally, cells have a property called contact inhibition, which means they stop growing when they come into contact with other cells. However, when this property is lost, cells can grow uncontrollably, leading to the formation of tumors.

2. **Role of Viruses in Tumor Formation**: Certain viruses can cause normal cells to become tumor cells. These viruses have specific genes that can alter the normal growth regulation of cells.

3. **Oncogenes**: The genes that are responsible for causing tumors are known as oncogenes. When a virus carries an oncogene, it is referred to as a viral oncogene (v-oncogene). This gene can induce the transformation of normal cells into cancerous cells.

4. **Proto-oncogenes**: In our body, there are also genes that can potentially cause cancer if they become activated. These are known as proto-oncogenes (c-oncogenes when they are inactivated). When a proto-oncogene is activated, it can lead to uncontrolled cell growth and cancer.

5. **Conclusion**: Therefore, a tumor-causing virus has viral oncogenes (v-oncogenes) that can convert normal cells into tumor cells.

**Final Answer**: Tumor-causing virus has viral oncogenes (v-oncogenes).

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