The Origin and Maturation of Germ Cells

The Origin and Maturation of Germ Cells
The vertebrate body is composed of nonreproductive somatic cells, which are differentiated for specialized functions and die with the individual, and germ cells, which form the gametes: eggs and sperm. Germ cells provide continuity of life between generations and ensure the species’ survival. Germ cells, or their precursors, the primordial germ cells, are set aside at the beginning of embryonic development, usually in the endoderm, and migrate to the gonads. Here they develop into eggs and sperm—nothing else. The continuity of germ cells from one generation to the next is called the germ cell line. The other cells of the gonads are somatic cells. They cannot form eggs or sperm, but they are necessary for the support, protection, and nourishment of the germ cells during their development (gametogenesis).

A traceable germ cell line, as present in vertebrates, is distinguishable in some invertebrates, such as nematodes and arthropods. In many invertebrates, however, germ cells develop directly from somatic cells at some period in the life of an individual.