heredities

Heredities are the processes by which traits are transmitted from parents to offspring. In biology, heredity encompasses genetic information in DNA and inherited features maintained by organelle genomes such as mitochondria and chloroplasts. Modern views also recognize epigenetic and related mechanisms that influence trait transmission across generations, contributing to non-genetic inheritance.

Hereditary information is organized into genes, which come in variants called alleles. Classical Mendelian inheritance describes how dominant and recessive alleles determine phenotypes in predictable patterns. Many traits are polygenic, shaped by multiple genes and environmental factors. Other patterns include codominance, incomplete dominance, and sex-linked inheritance, where genes on sex chromosomes follow different rules. Genetic recombination during meiosis and mutation introduce new variation.

Organellar inheritance follows different rules from nuclear genes. Mitochondrial DNA is typically inherited from the mother in many animals, while chloroplast DNA is inherited in various ways in plants. Epigenetic marks—chemical modifications of DNA or chromatin—can also influence gene expression in offspring and may be transmitted across generations, contributing to heritable variation beyond DNA sequence.

Historically, heredities were studied through selective breeding, leading to the concept of genes. Gregor Mendel’s pea experiments in the 19th century established the basic patterns of inheritance, later integrated with the chromosome theory. The discovery of DNA and the decoding of genomes transformed heredity into molecular genetics and genomics, enabling mapping, sequencing, and prediction of inherited traits.

Understanding heredities informs medicine, agriculture, and evolutionary biology. It underpins genetic counseling, diagnosis of heritable diseases, and plant and animal breeding. Yet trait expression results from gene–environment interactions, regulatory networks, and epigenetic factors, so heredity sets probabilities rather than certainties.