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.
During this stage, all of your baby's major organs and body parts begin to develop. The cells of the embryo (called embryonic stem cells) multiply and change into the hundreds of different types of cells needed to make a whole human body.The placenta also develops during the embryonic stage. This is one of the first things to develop during the embryonic stage. 2  This means your babyâs brain, spinal cord and nerves form during this stage. 3  Heart. 4  An S-shaped tube forms on the front of the embryo.