Flexi Says: A complex phenotype is the consequence of complex interactions of a large number of genetic and non-genetic determining factors. Such traits show a continuous range of variation and are influenced by both environmental and genetic factors. In human genetics which are controlled by multiple genes and whose inheritance does not follow the rules of Mendelian genetics. Such traits are known as complex traits. Complex traits are believed to result from gene-gene and gene-environment interactions, genetic heterogeneity, and potentially other yet unknown reasons.