Female sperm can refer to those that carry an X chromosome and, after fertilization, result in a female baby, but it can also refer to the theoretical concept of making sperm from female cells instead of male cells. While female sperm are not yet scientifically achievable as of 2011, scientists have managed to make sperm-like structures from stem cells. If sperm are able to be engineered from stem cells, then stem cells from a woman may be suitable as the basis for this technique. Female sperm could therefore result in a baby that does not contain any genetic material from a male but only from women.
Normally, male organisms produce sperm, and female organisms produce eggs. Humans need two matching sets of 23 chromosomes to make up a healthy person. A woman has duplicate versions of 22 chromosomes in common with a man. She has two X chromosomes, however, where a man has one X and one Y chromosome. The presence or absence of a Y chromosome, therefore, dictates whether a person is male or female.
Each egg from a woman contains one half of the genetic material necessary to create a normal person. The other half comes from the sperm. Some sperm have 23 chromosomes including an X chromosome, and some have 22 chromosomes with a Y chromosome. When an X-carrying sperm, sometimes also called a female sperm, fertilizes the egg, the resultant baby is female, and when a Y-carrying chromosome fertilizes the egg, the baby is male.
Only men produce sperm as only men have the Y chromosome to supply the sperm that could make a male baby. Certain genes on the Y chromosome are also thought to play essential roles in sperm production, and women's cells do not have these genes. Scientists, therefore, previously thought that making sperm from women's cells was impossible.
A possible way of making female sperm arose, however, when Professor Karim Nayernia of Newcastle University in the U.K. created sperm-like cells using stem cells as the raw material. In 2006, the team obtained cells from a mouse embryo. In early life, embryonic cells can turn into many different cell types and act as the "stem" from where many forms of cells branch off.
The team treated the embryonic cells with a chemical that made them grow and divide into sperm-like cells. A portion of these cells then became sperm-like, with a head, tail, and half the chromosomes necessary for life, just like regular sperm. They were even capable of fertilizing mouse eggs, which grew into live mouse pups.
Humans past the stage of embryos also have stem cells in various parts of the body. Bone marrow is one area where the cells still have the capability of growing into different types. More experiments at Newcastle University proved that male bone marrow could grow into cells that resembled sperm and that had the necessary 23 chromosomes. Female embryonic stem cells also produced the same type of cells, according to the research team.
Scientific opinion, as of 2011, is still divided about whether these stem cell-derived cells are capable of fulfilling the role of sperm and properly fertilizing an egg to create a child. The procedure is still theoretical. If female sperm were effective at fertilizing eggs, then men would no longer be essential to the creation of a baby, and people like lesbian couples could combine their own, entirely female, genes to make a child.