Name first transgenic animal. For which gene was it genetically modified?

Explanation

**Step-by-Step Solution:**

1. **Identify the First Transgenic Animal**: The first transgenic animal created was a mouse. This was achieved in 1974 by Rudolf Jaenisch.

2. **Understand the Genetic Modification**: The transgenic mouse was genetically modified by introducing foreign DNA into its embryo. This process involved inserting an extra gene into the mouse's DNA.

3. **Identify the Gene Modified**: The specific gene that was introduced into the transgenic mouse was related to the HSB-TK enzyme activity. This gene was known to be activated by metals and influenced the expression of the endogenous MT1 gene in the liver of the transgenic mice.

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