Another type of stem cell that has properties similar to the embryonic stem cell is the embryonic germ cell, derived from the early stages of the developing fetus. (NBAC) Often, stem cells are lumped together into one category for the sake of ease. However, to fully understand the nature of this, it is important to understand that all stem cells do not share common characteristics or sources and it is important to know the difference between various types of cells. The main focus of the controversy is the stem cell derived from human embryos. Although stem cells have been harvested from adults "Adult stem cells" they are not considered an alternative to embryos because they are limited in their ability to form various cells. .
Embryonic stem cell research has been controversial due to the reason that these cells come from human embryos or fetal tissue. Embryonic stem cells can be harvested by number of methods. The first method, which is primarily used is from embryos created by invitro-fertilization as a method of overcoming infertility that are later donated by couples that no longer had plans to use the embryos. This method collects embryonic stem cells. The second method, which is also currently employed, at a lesser frequency, is the collection of human fetal tissue following an elective abortion. By this method, embryonic germ cells are collected. The creation of embryos by invitro-fertilization with gametes (sex cells) donated for the sole purpose of providing stem cells is another possible way of collecting cells, yet this methods has been strongly debated due to it's sensitive nature. (NBAC).
After the extraction of the embryos, the stem cells must be created. To create embryonic stem cells for research, a "stem cell line" must be created form the inner cell mass of a week-old embryo. A stem cell line is a mass of cells derived from the original, sharing its genetic characteristics.