private static void GenerateNegZMutation(BuildingLot _lot)
    {
        List <Panel> addedPanels = new List <Panel>();

        // set new height, width and length
        // Calculate size of mutation

        int newHeight = (int)_lot.GetCurrentBuildingHeight() / 2;

        newHeight = (int)Random.Range(newHeight, _lot.GetCurrentBuildingHeight());

        if (newHeight <= 1)
        {
            return;
        }

        _lot.SetCurrentBuildingHeight(newHeight);

        int newWidth = (int)Random.Range(1, (_lot.GetNegZWidth() + 1));

        int newLength = (int)Random.Range(1, _lot.GetOffsetZ() + 1);

        if (newWidth == 1)
        {
            return;
        }

        // Generate panels!
        Vector3 pos = _lot.transform.position + new Vector3(_lot.GetOffsetX(), 0.0f,
                                                            _lot.GetOffsetZ() + (float)panelSize / 2 - newLength);

        GenerateNegXPanels(_lot, newLength, pos, addedPanels);

        pos = _lot.transform.position + new Vector3(_lot.GetOffsetX() + newWidth, 0.0f,
                                                    _lot.GetOffsetZ() + (float)panelSize / 2 - newLength);

        GeneratePosXPanels(_lot, newLength, pos, addedPanels);

        pos = _lot.transform.position + new Vector3(_lot.GetOffsetX() + (float)panelSize / 2,
                                                    0.0f, _lot.GetOffsetZ() - newLength);

        GenerateNegZPanels(_lot, newWidth, pos, addedPanels);

        pos = _lot.transform.position + new Vector3(_lot.GetOffsetX() + (float)panelSize / 2,
                                                    0.0f, _lot.GetOffsetZ());

        GeneratePosZPanels(_lot, newWidth, pos, addedPanels);

        pos = _lot.transform.position + new Vector3(_lot.GetOffsetX() + (float)panelSize / 2,
                                                    newHeight - (float)panelSize / 2, _lot.GetOffsetZ() - newLength + (float)panelSize / 2);

        GeneratePosYPanels(_lot, newWidth, newLength, pos, addedPanels);

        if (newWidth == _lot.GetNegZWidth())
        {
            _lot.SetNegXWidth(_lot.GetNegXWidth() + newLength);
            _lot.SetPosXWidth(_lot.GetPosXWidth() + newLength);

            _lot.SetOffsetZ(_lot.GetOffsetZ() - newLength);
        }

        MergeList(_lot, addedPanels);
    }