How do germ cells differ structurally and genetically?
Answers
Germ cells are the embryonic precursors of the gametes. They are set aside from the somatic cell lineages early in the development of most species. In the mouse. the germ cells, once they have formed, migrate through the tissues of the embryo to the gonad primordia (genital ridges), where they coassemble with somatic gonadal cells to form the sex cords. (See Fig. 1 for a scheme of germ cell formation and migration.) The sex cords are the forerunners of the seminiferous tubules of the male gonad or the ovarian follicles of the female gonad. They become sexually dimorphic as they form in the mouse embryo, between embryonic day 11.5 (E 11.5) and E12.5. In addition to their complex differentiation into eggs and sperm, germ cells retain the property of pluripotency, which is required for the gametes to differentiate into new individuals. Germ cells that do not enter the gonad primordia can develop into germ line tumors later in life. Errors in germ cell differentiation can lead to infertility.
Germ eells are the only cell
s in structurally and genetically the body to undergo meiotic cell divisions during their differentiation. This leads to haploidy of the gametes and also generates genetic differences between individuals. Errors of meiotic recombination lead to aneuploidy and to congenital disorders in the offspring. In many species, the differentiation of the female gametes includes the synthesis and storage of molecules (known as cytoplasmic determinants) that control early growth and patterning of the ensuing embryo. The degree to which early development is patterned maternally varies widely between species. In many species, the formation of the germ line itself is controlled by maternal cytoplasmic determinants. that'why germ cells differ