1 James Watson and Francis Crick discovered the double helix in 1953. 2  In 2003, scientists completed the Human Genome Project.  DNA today can tell us everything from paternity to risk factors for chronic disease.
The genetic material of the sperm and egg then combine to form a single cell called a zygote and the germinal stage of prenatal development commences. Embryogenesis covers the first eight weeks of development and at the beginning of the ninth week the embryo is termed a fetus.Human embryology is the study of this development during the first eight weeks after fertilisation. The normal period of gestation (pregnancy) is nine months or 38 weeks.n comparison to the embryo, the fetus has more recognizable external features, and a more complete set of developing organs. The entire process of embryogenesis involves coordinated spatial and temporal changes in gene expression, cell growth and cellular differentiation.
All of the processes of embryo development are described by the term embryogenesis. The embryo is called a fetus after the completion of this stage of development. The stage of prenatal development that occurs from the end of the embryonic period until birth is called the fetal period.The most notable development during this stage is the dramatic change in size that takes place. This is the baby's final preparation for life outside the womb.hink of Steve and Jennifer's baby as spending the germinal period looking for a place to live. Now that she's found her place, she's ready to start organizing for the work she has ahead of her. This is the embryonic period of prenatal development.