Basic principles of Genetics

Abstract

Genetic disease may be caused by defects in one gene (Mendelian or monogenic diseases) or more than one gene (polygenic diseases), but it can also be a result of the interaction of environmental and genetic factors (complex or multifactorial traits) The major Mendelian patterns of inheritance are autosomal recessive (e.g. oculocutaneous albinism), autosomal dominant (e.g. Darier disease), X-linked recessive (e.g. hypohidrotic ectodermal dysplasia), and X-linked dominant (e.g. incontinentia pigmenti). Factors modifying the basic Mendelian pattern of inheritance include incomplete penetrance, age-dependent penetrance, variable expression, de novo mutations, pseudodominant inheritance, genomic imprinting, and mitochondrial inheritance. Chromosomal anomalies can consist of abnormalities in the number (e.g. polyploidy, aneuploidy) or in the structure (e.g. translocations, …)