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These PGCs will later give rise to germline sperm cells or egg cells. At this point the PGCs have high typical levels of methylation. Then primordial germ cells of the mouse undergo genome-wide DNA demethylation, followed by subsequent new methylation to reset the epigenome in order to form an egg or sperm. [25]
After this fertilization event occurs, germ cells divide rapidly to produce all of the cells in the body, causing this mutation to be present in every somatic and germline cell in the offspring; this is also known as a constitutional mutation. [2] Germline mutation is distinct from somatic mutation.
In 2004, considerable evidence was provided for the existence of germline stem cells in adult mouse ovaries capable of generating oocytes to form new follicles. [11] [12] [13] Questions exist about cell-sorting techniques used to isolate the OSCs, [14] and some researchers prefer the less-conclusive term "female germline stem cells" to "OSCs". [15]
PGC-like cells generated using this method can be transplanted into a gonad, where the differentiate, and are able to give viable gametes and offspring in vivo. [34] PGC-like cells can also be generated from naïve embryonic stem cells (ESCs) that are cultured for two days in the presence of FGF and Activin-A to adopt an epiblast-like state.
In addition, stem cell are undifferentiated cells which can develop into a specialized cell and are the earliest type of cell in a cell lineage. [2] Due to the differentiation in function, somatic cells are found only in multicellular organisms, as in unicellular ones the purposes of somatic and germ cells are consolidated in one cell.
Many organisms simply do not dedicate a separate germline during early development. Plants and basal animals such as sponges and corals instead generate gametes from pluripotent stem cells in adult somatic tissues. [7] [8] In flowering plants, for example, germ cells can arise from adult somatic cells in the floral meristem.
The idea that germline cells contain information that passes to each generation unaffected by experience and independent of the somatic (body) cells, came to be referred to as the Weismann barrier, and is frequently quoted as putting a final end to the theory of Lamarck and the inheritance of acquired characteristics. What Lamarck claimed was ...
Whatever may happen to those cells does not affect the next generation. The Weismann barrier , proposed by August Weismann , is the strict distinction between the "immortal" germ cell lineages producing gametes and "disposable" somatic cells in animals (but not plants), in contrast to Charles Darwin 's proposed pangenesis mechanism for inheritance.