Embryo, Embryo

In humans, it is called an embryo until about eight weeks after fertilization (i.e. ten weeks LMP), and from then it is instead called a fetus.

In organisms that reproduce sexually, once a sperm fertilizes an egg cell, the result is a cell called the zygote that has half of the DNA of each of two parents. The resulting embryo derives 50 percent of its genetic makeup from each parent. 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.

However, the position and arrangement of the germ layers are highly species-specific, depending on the type of embryo produced. In vertebrates, a special population of embryonic cells called the neural crest has been proposed as a "fourth germ layer", and is thought to have been an important novelty in the evolution of head structures.

The cerebrum in humans, which is the most sophisticated part of the brain, develops last. This rule is not absolute, but it is recognized as being partly applicable to development of the human embryo.

Organogenesis and growth continue. Hair has started to form along with all essential organs. Facial features are beginning to develop. At the end of the 8th week, the embryonic stage is over, and the fetal stage begins.

They include selective reduction, prenatal diagnosis, preimplantation diagnosis, invitro fertilization, cryopreservation, emergency contraception, parahumans, embryo transfer, genetic engineering and embryo donation that have been criticized as unethical by some pro-life ethicists. A summary of the embryonic ethical controversies, from a Roman Catholic perspective, can be found in the Vatican document Dignitas Personae , published in Rome in 2008.

Current medical technology does allow an embryo to be transplanted from the uterus of one woman to that of another. Rumbold, Graham.

Stem cell research, reproductive cloning, and germline engineering are all currently being explored. The morality of this research is also debated because an embryo is commonly destroyed. Freedman, Jeri. "America Debates Stem Cell Research." New York, NY: The Rosen Publishing Group, 2008.

Source: Wikipedia > Embryo