Somatic cell

In cellular biology, a somatic cell—also called a vegetal cell—is any cell that makes up the body of a multicellular organism, excluding gametes, germ cells, gametocytes, and undifferentiated stem cells. These cells form an organism’s tissues and organs and reproduce through mitosis. In mammals, somatic cells constitute all internal organs, skin, bones, blood, and connective tissue, while germ cells produce sperm and eggs. There are about 220 distinct types of somatic cells in the human body.

Unlike germ cells, which give rise to gametes through meiosis, somatic cells do not pass their mutations to an organism’s offspring—only to their own cellular descendants. However, in sponges, undifferentiated somatic cells can form the germ line, and in Cnidaria, differentiated somatic cells can serve as the source of the germ line. Mitotic division occurs only in diploid somatic cells; only certain cells, such as germ cells, are involved in reproduction.

Evolutionarily, sterile somatic cells have arisen multiple times as multicellularity evolved. The separation between an immortal germline and specialized somatic cells introduced mortality, a pattern seen simply in volvocine algae. Species with this separation are called Weismannists, a relatively rare condition found in vertebrates, arthropods, and *Volvox*. Many other organisms—such as land plants, most algae, and numerous invertebrates—retain the ability for somatic embryogenesis.

Genetically, somatic cells contain DNA arranged in chromosomes. When chromosomes occur in pairs, the cell is diploid, and the organism is diploid. In humans, somatic cells have 46 chromosomes in 23 pairs—one from each parent. Gametes, by contrast, are haploid, containing 23 unpaired chromosomes. Upon fertilization, two gametes fuse to form a zygote with 46 chromosomes. Many species have somatic cells with chromosomes in sets of four (tetraploid) or six (hexaploid), and their germline cells may be diploid or triploid. For example, cultivated wheat (*Triticum aestivum* L.) is hexaploid, with six copies of each chromatid in its somatic cells.

Spontaneous mutation rates are significantly lower in advanced male germ cells than in somatic cells from the same individual. Female germ cells also show a lower mutation frequency than somatic cells, similar to that of male germ cells. This suggests that germ cells employ more effective mechanisms—likely including elevated DNA repair enzyme levels—to limit initial mutations.

Cloning of whole mammals has been achieved using somatic cell nuclear transfer. In this technique, the nucleus from a somatic cell (often a skin cell) is removed and injected into an ovum of the same species that has had its own genetic material removed. The ovum, now containing a diploid set of chromosomes, does not need fertilization and can be implanted into a uterus to develop. The resulting animal is a nearly identical genetic clone of the nucleus donor, differing only in mitochondrial DNA from the ovum. While the technique has been problematic in practice, notable successes include Dolly the Sheep and Snuppy, the first cloned dog.

In biobanking, somatic cells are collected and cryopreserved to conserve animal genetic resources as biodiversity declines. The goal is to store viable cells long-term, with the hope that they can later be reprogrammed into induced pluripotent stem cells (iPSCs) and then into viable reproductive cells.

Biotechnology has enabled genetic modification of somatic cells, used for modeling chronic diseases or preventing certain conditions.