A germ cell is part of the germline and is involved in the reproduction of organisms. Germ cells should not be confused with "germs" (pathogens). The germ cells in male and female humans are gametes, the sperm and ova respectively, along with the gonocytes. They are also called sex cells, but that term is also often used to refer only to gametes or a zygote.
Germ cells includes all stages of gametogenesis, i.e. the gonocytes, gametogonia, gametocytes, gametids, and the gametes. By a narrower definition, the term germ cell can also just refer to gametes, which are produced by meiosis of the aforementioned germ cells, but this definition is less precise. Cells that are not part of the germline are somatic cells.
Primordial germ cells are predecessors of germ cells. They migrate to the gonadal ridge, where they form gametogonia, and thus start gametogenesis. See: Germ line development.
Normal human somatic cells are diploid, which means they contain 23 pairs of chromosomes, including one pair of sex chromosomes; an X from the mother, and an X or a Y from the father. If the sex chromosomes are XX then the organism is female and if they are XY then the organism is male. Human germ cells are normally haploid, which means they contain half the chromosomes of somatic cells, or 23 chromosomes including one of the sex chromosomes. Thus when the germ cells unite in fertilization, the cell becomes diploid, and commences embryogenesis.
Genetic therapy, where new genetic material is introduced into an organism, usually confers new, genetic instructions for a cell and its daughter cells, and the new genetic information dies with the organism. When the genetic material is put into a germ cell, the new genetic information (for better or worse) may be transferred to biological offspring.
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