monogenen

Monogenen is a term used in genetics to describe traits and conditions that are determined by a single gene locus. In classical usage, monogene traits follow Mendelian inheritance and can be autosomal dominant, autosomal recessive, or X-linked, depending on the chromosome and the nature of the allele involved. The resulting phenotypes often show predictable patterns within families, such as typical 3:1 or 1:1 ratios in offspring from certain crosses, assuming complete penetrance and no additional genetic or environmental modifiers.

Penetrance and expressivity influence how a monogene trait appears in individuals. Penetrance refers to the proportion of individuals with the causal genotype who actually express the trait; incomplete penetrance means some carriers do not. Expressivity describes the range of trait severity among those who express it. While many monogenic disorders present with clear phenotypes, some show variability in age of onset, severity, or symptom spectrum.

Examples of monogenic disorders include cystic fibrosis (autosomal recessive), Huntington’s disease (autosomal dominant with high penetrance and late onset), and phenylketonuria (autosomal recessive). It is important to distinguish monogenic traits from polygenic traits, which arise from the combined effects of multiple genes and often interact with environmental factors.

Advances in sequencing and genetic analysis have improved identification and understanding of monogene traits, aiding genetic counseling, carrier testing, and research into gene function and disease mechanisms.