List factors which may complicate interpretation of the pattern of inheritance in a pedigree. Describe the meaning and clinical implications of the Lyon hypothesis and its relation to carrier status in X-linked disorders. Define mosaicism and describe the clinical consequences of germline mosaicism. Describe uniparental disomy and genetic imprinting and their potential clinical consequences.
Genetic heterogeneity characterizes many genetic disorders.
Allelic heterogeneity is used to describe the situation when several different mutations at a single locus can cause the same or similar expression. Locus heterogeneity pertains when mutations at different loci or different type of genetic and sometimes non-genetic mechanisms can result in the same or similar expression. In both cases, similar phenotypes are caused by different genotypes. Penetrance is the probability that a gene will have any phenotypic expression. Exceptions, showing .