Germline

Germline refers to the lineage of reproductive cells that pass genetic information to offspring. In animals, the germline includes primordial germ cells and the gametes they produce—sperm and eggs. It is distinguished from somatic cells, which form the body's tissues and organs and do not transmit genetic information to the next generation. In plants, the concept is similar but the formation of the germline can occur later in development, with reproductive cells arising from various tissues.

Development and transmission: In humans and many other organisms, primordial germ cells arise early in embryogenesis and migrate to the developing gonads, where they differentiate into spermatogonia in males and oogonia in females. Through meiosis, these cells generate haploid gametes. Fertilization combines two gametes to form a diploid zygote, which contains the germline genome and develops into a new organism. Genetic changes in germline cells, known as germline mutations, can be passed to offspring and are therefore heritable.

Germline mutations and editing: Germline mutations can underlie inherited diseases and also contribute to evolutionary variation. Because they are transmitted to all cells of the offspring, they carry implications for future generations. Germline genome editing—altering the DNA of germ cells or embryos—raises substantial safety, ethical, and regulatory concerns and is subject to legal restrictions in many jurisdictions. In contrast, somatic mutations and somatic gene therapies affect only the treated individual and are not inherited.