Display data in ASP.Net GridView on DropDownList change without page refresh using UpdatePanel

I have a dropdown list containing values 

ValueA

ValueB

Required output

When I select the valueA or any value from dropdown list it should display data in Gridview without page refresh. I wrote the following code

HTML

<div class="col-sm-3">
    <asp:UpdatePanel ID="SCPanel" runat="server" UpdateMode="Conditional" ChildrenAsTriggers="false">
        <ContentTemplate>
            <label class="control-label" style="margin-top: 10px;">Branch</label>
            <asp:DropDownList ID="ddlBranch" runat="server" class="validate[required] form-control"
                AutoPostBack="True" OnSelectedIndexChanged="ddlBranch_SelectedIndexChanged">
            </asp:DropDownList>
        </ContentTemplate>
    </asp:UpdatePanel>
</div>

protected void ddlBranch_SelectedIndexChanged(object sender, EventArgs e)
{
    this.BindSection();
}
protected void BindSection()
{
    GridView1.Visible = true;
    con = new SqlDbConnect();
    con.SqlQuery("select AdmissionNo,RollNo,ClassName,SectionName,SName,FName,DOB,SPic from tblStdReg as sr inner join tblDefClass as dc on sr.ClassID=dc.ClassID inner join tblDefSection as ds on sr.SectionID=ds.SectionID where sr.ClassId=@CId and sr.SectionId=@SId order by RollNo, AdmissionNo");
    con.Cmd.Parameters.Add(new SqlParameter("@CId", this.ddlClass.SelectedValue));
    con.Cmd.Parameters.Add(new SqlParameter("@SId", this.ddlSection.SelectedValue));
    adapt.SelectCommand = con.Cmd;
    adapt.Fill(sTable);
    if (sTable.Rows.Count > 0)
    {
        GridView1.Visible = true;
        GridView1.DataSource = sTable;
        GridView1.DataBind();
        lblTotal.Text = GridView1.Rows.Count.ToString();
    }
    else
    {
        GridView1.Visible = false;
        ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('No Record Found');", true);
        lblTotal.Text = "0";
        return;
    }
    con.conClose();
}

but nothing happened or it is showing nothing. How to get solution plz