Value of the Backcross Parental Lines Variable Indicating the Parental Line 2 Use this text box to specify the value of the Backcross Parental Lines Variable that indicates which line is the parental line 2 for the backcross. To Specify the Value of the Backcross Parental Lines Variable: Enter the value in the text box. If you change your mind and would like to reset the field, click Clear.