Single-Gene Disorders: Inheritance Patterns, Phenotype Variability, and Allele Frequencies

Genes are functional units of DNA that make some product needed by cells, either the polypeptide chain of a protein or a functional noncoding RNA. In this chapter, however, we will consider genes very largely as abstract entities and we consider them within the context of singlegene disorders-diseases in which the genetic contribution is determined primarily by one gene locus. Although individually rare, single-gene disorders are important contributors to disease. Knowledge of single-gene disorders also provides a framework for understanding the more complex genetic susceptibility to common disease (which we cover in later chapters, notably Chapters 8 and 10).