I want to be able to validate whether or not, male/female has been selected or if it hasn't been selected. Here's the code I have: 

protected void checkGender()
    {
        var selectedGender = ddlGender.SelectedValue;
 
        if(selectedGender == "-1")
        {
           
Label1.Text = "Please select your gender!";
        }
        else
        {
           
Label1.Text = "";
        }
    }
<asp:DropDownList ID="ddlGender"runat="server">
  <asp:ListItem Value="-1">Please select...</asp:ListItem>
  <asp:ListItem Value="Male">Male</asp:ListItem>
  <asp:ListItem Value="Female">Female</asp:ListItem>
</asp:DropDownList>