Don't use the 'for' and 'id' attribute in the <label> and <input> tags.
Try this code:
<div>
<label>Gender</label><br/>
<input type="radio" name="gender" />
<label>Male</label><br/>
<input type="radio" name="gender" />
<label>Female</label><br/>
<input type="radio" name="gender"/>
<label>Other</label><br/>
</div><br/>