embryo

An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of fertilization until birth, hatching, or germination. In humans, an embryo is generally considered to be between the first and the eighth week of development after fertilization and from then it is instead called a fetus. Some definitions consider embryological life to start at the third week of development to the eighth, when most organ systems are developing. The development of the embryo is called embryogenesis. In organisms that reproduce sexually, once a sperm fertilizes an egg cell, the result is a cell called the zygote, which possesses half the DNA of each of its two parents. In plants, animals, and some protists, the zygote will begin to divide by mitosis to produce a multicellular organism. The result of this process is an embryo.