Читать книгу Human Developmental Biology - Danton Inc. O'Day - Страница 4

Primordial germ cells (PGCs) are the source of sperm and eggs. They are specialized cells that are localized in our ovaries and testes. The primordial germ cells give rise to the male and female sex cells which in turn transmit the genome from generation to generation. The “Saga of the Sex Cells” is a true tale of cellular struggle, long journeys and tragic events. The future eggs and sperm are critical to the survival of each species. As a result, in some species, their fate is determined long before the egg begins to divide. Special factors (determinants) dictate that the cells that contain them will become sex cells. The cells that acquire these determinants then have a long haul ahead. First they must migrate through the embryonic tissues to the sites where the future gonads will form.

Along the way some will get lost and simply die. Other lost cells will not accept their inability to get to where they were supposed to and will begin to develop inappropriately forming dangerous malignant tumors called teratomas. Those that do arrive safely will have to wait many long years as the genital ridges first develop into gonads and then, at puberty, become functional producers of mature gametes. In the ovaries, a limited supply of eggs will be produced that will have to suffice for the life of the female while in the male sperm production will be a continuous process that can last until death. The way in which eggs and sperm form and the differences in their formation are equally interesting and reflect the important role each has in ensuring that successful fertilization will result so that the next generation will begin.