J节段 （连接节段） 是免疫球蛋白和T细胞受体基因座中的编码串行。J节段介于可变基因节段（V） 和恒定基因节段（C） 之间。

V(D)J recombination, less commonly known as somatic recombination, is the unique mechanism of genetic recombination that occurs only in developing lymphocytes during the early stages of T and B cell maturation. The process results in the highly diverse repertoire of antibodies/immunoglobulins (Igs) and T cell receptors (TCRs) found on B cells and T cells, respectively. The process is a defining feature of the adaptive immune system and its development was a key event in the evolution of jawed vertebrates.