recombination, in genetics, primary mechanism through which variation is introduced into populations. Recombination takes place during meiosis, when maternal and paternal genes are regrouped in the formation of gametes (sex cells). Recombination occurs randomly in nature as a normal event of meiosis and is enhanced by the phenomenon of crossing over, in which gene sequences called linkage groups are disrupted, resulting in an exchange of segments between paired chromosomes that are undergoing separation. Thus, although a normal daughter cell produced in meiosis always receives half of the genetic material contained in the parent cell (i.e., is haploid), recombination acts to ensure constant variability: no two daughter cells are identical, nor are any identical in genetic content to the parent cell.

Laboratory study of recombination has contributed significantly to the understanding of genetic mechanisms, allowing scientists to map chromosomes, identify linkage groups, isolate the causes of certain genetic anomalies, and manipulate recombination itself by transplantation of genes from one chromosome to another. Because of its potential for creating new—and possibly pathogenic—organisms, experimental recombination can have potentially negative consequences for human health and the health of the environment. The generation of proprietary organisms, such as disease-resistant plants available from only a single producer, has further raised ethical questions for various industries, particularly in the area of agriculture.