C sharp - checkbox en datagridview

if (agregocol)

{

    this.dataGridViewAgenda.Columns.Remove("chk");

}

DataGridViewCheckBoxColumn checkboxColumn = new DataGridViewCheckBoxColumn();

checkboxColumn.Width = 30;

checkboxColumn.Name = "chk";

checkboxColumn.HeaderText = "SelCelular";

checkboxColumn.Visible = true;

checkboxColumn.DisplayIndex = 8;

checkboxColumn.Frozen = false;

// checkboxColumn.FlatStyle = FlatStyle.Standard;

checkboxColumn.DefaultCellStyle.Alignment = DataGridViewContentAlignment.MiddleCenter;

checkboxColumn.ReadOnly = false;

this.dataGridViewAgenda.Columns.Add(checkboxColumn);