 
     # chartOpts start
     chrGap = chartOpts?.chrGap ? 6 # gap between chromosomes in pixels
+    oneAtTop = chartOpts?.oneAtTop ? false # if true, put chromosome 1 at the top rather than bottom
     colors = chartOpts?.colors ? ["slateblue", "white", "crimson"]  # vector of three colors for the color scale (negative - zero - positive)
     nullcolor = chartOpts?.nullcolor ? "#e6e6e6" # color for empty cells
     zlim = chartOpts?.zlim ? null # z-axis limits (if null take from data, symmetric about 0)

                 .attr("stroke", "none")
                 .attr("stroke-width", "1")
                 .on("mouseover.paneltip", (d) ->
                                               d3.select(this).attr("stroke", "black")
                                               celltip.show(d))
                 .on("mouseout.paneltip", () ->
                                               d3.select(this).attr("stroke", "none")
                                               celltip.hide())

    # functions to grab stuff

                            z = d3.format(".2f")(Math.abs(d.lod))
                            px = formatAxis(posByChr[d.chrx])(d.posx)
                            py = formatAxis(posByChr[d.chry])(d.posy)
                            "(#{d.chrx}@#{px},#{d.chry}@#{py}) &rarr; #{z}")
                    .direction('e')
                    .offset([0,10])
        svg.call(celltip)
