Furthermore, homophily, the tendency for couples to pair on the basis of shared attributes (including sub-clinical disease indicators), will tend to enrich for variants that promote those attributes104. Granularity of traits is difficult to document, but facial features provide a good example of a suite of traits that do not simply follow either blending or Mendelian inheritance105. Certain features such as the shape of the nose, location of the cheek bones, or curve of the lips, run strongly in families, appearing in distant relatives in patterns that are suggestive of large genetic effects. If such clustering is also true of endophenotypes then the infinitesimal model will be incomplete.
