This process is known as meiosis. The precursor cells that eventually turn into either eggs or sperm is known as germ cells. They are identical both in male and female embryos. Professor Koopman said that in females, meiosis begins before birth and eggs are produced, whereas in males, meiosis begins after birth and the result is sperm. Retinoic acid, a derivative of Vitamin A, causes germ cells in female embryos to begin meiosis, leading to the production of eggs. In the case of males an enzyme is present in male embryos that wipes out retinoic acid and so suppresses meiosis before birth, resulting in sperm production.
Further research is to be carried to figure out what triggers and suppresses meiosis. This would later help the researchers to improve fertility. Professor Koopman also said that an inappropriate retinoid signal might give the wrong instructions to germ cells, which could lead to the formation of germ cell tumors. Researchers said that further investigation is necessary so that one day it would lead to a cure.