Human digestive system digestive system is subject to a wide range of disorders many of which can be congenital. Mouth diseases can also be caused by pathogenic bacteria, viruses, fungi and as a side effect of some medications. Mouth diseases include tongue diseases and salivary gland diseases. A common gum disease in the mouth is gingivitis which is caused by bacteria in plaque. The most common viral infection of the mouth is gingivostomatitis caused by herpes simplex. A common fungal infection is candidiasis commonly known as "thrush" which affects the mucous membranes of the mouth. There are a number of esophageal diseases such
Human disease modifier gene phenotype of interest. Thus, the first step of establishing the likelihood that modifier genes indeed exist and contribute to observed variation is crucial to this described research process. This is typically done by eliminating other sources of heterogeneity as likely causes of the phenotypic variation in the disease of interest. Recalling Haldane's model, these sources of are generally classified as 1) genetic variation in the major locus 2) other sources of genetic heterogeneity, which include but are not limited to modifier genes, and 3) environmental influences. Crucial to the efficient study of the molecular basis of human genetic disease via