Heredity

Heredity is the passing of traits from parents to offspring through genetic material. It explains why related individuals resemble each other and why offspring vary from their parents. In most organisms, hereditary information is stored in DNA within chromosomes; in some viruses, it is RNA. Genes, which are specific segments of DNA, influence development, physiology, and behavior, while environmental factors can modify trait expression.

Historically, heredity gained formal study with Gregor Mendel, whose pea plant experiments in the 1860s revealed that inheritance occurs through discrete units now called genes, with patterns of dominant and recessive alleles and the segregation of parental alleles. The chromosomal theory in the early 20th century linked genes to chromosomes, and later work established DNA as the molecular basis of heredity.

Genes reside on chromosomes and exist in different forms, called alleles. In simple Mendelian cases, a dominant allele masks a recessive one in heterozygotes. Other patterns include incomplete dominance, where the phenotype is intermediate, and codominance, where both alleles are expressed. Many traits are polygenic, shaped by multiple genes and often showing continuous variation. Mutations create new alleles, while recombination and linkage affect how traits are inherited together. Epigenetic changes can alter gene expression without changing DNA sequence.

The study of heredity informs medicine, agriculture, and evolutionary biology. Applications include genetic counseling, screening, and selective breeding. The concept also encompasses the role of environment in phenotype and how inherited variation drives evolution through natural selection.