In a class that I'm taking we were presented 3 types of stem cells.
- Adult stem cells which come from bone marrow
- Embryonic stem cells which come from embryos
- Embryonic germ cells which come from testes
I understand that adult stem cells are a bit more specialized than embryonic stem cells, but I'm confused why embryonic germ cells are considered stem cells. From Wikipedia, the definition of stem cells is:
Undifferentiated biological cells that can differentiate into specialized cells and can divide (through mitosis) to produce more stem cells
But from my limited understanding of biology embryonic germ cells can't specialize into any other cells unless they fuse with another gamete, so why would they be considered stem cells? What am I missing here?