   randomDraw = (x) -> x[Math.floor(Math.random()*x.length)]
 
   randomChr = randomDraw(data.chr)
-  randomMarker = randomDraw(data.markers[randomChr])
+  randomMarker = maxLodByChr_marker[randomChr]
 
   # initial phenotype vs genotype plot
   initialPXG = (chr, marker) ->

                          .attr("stroke", "black")
                          .attr("stroke-width", "1")


  # chr labels
  topsvg.append("g").attr("id", "chrLabels").selectAll("empty")

  for i in data.chr
    currentMax = d3.max(data.lod[i].lod)
    maxLod = currentMax if maxLod < currentMax

  # for each chromosome, find the marker with maximum LOD score
  maxLodByChr = {}
  maxLodByChr_marker = {}
  for i in data.chr
    maxLodByChr[i] = 0
    maxLodByChr[i] = ""
    for m of data.markerindex[i]
      lod = data.lod[i].lod[data.markerindex[i][m]]
      if lod > maxLodByChr[i]
        maxLodByChr[i] = lod
        maxLodByChr_marker[i] = m

  # maximum effect + SE and minimum effect - SE
  effMax = null
