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.
Child development stages are the theoretical milestones of child development, some of which are asserted in nativist theories. This article discusses the most widely accepted developmental stages in children. There exists a wide variation in terms of what is considered normal, caused by variation in genetic, cognitive, physical, family, cultural, nutritional, educational, and environmental factors. Many children reach some or most of these milestones at different times from the norm. Holistic development sees the child in the round, as a whole person - physically, emotionally, intellectually, socially, morally, culturally and spiritually. Learning about child development involves studying patterns of growth and development, from which guidelines for 'normal' development are drawn up.