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The normal period of gestation (pregnancy) is about nine months or 36 weeks. The germinal stage refers to the time from fertilization through the development of the early embryo until implantation is completed in the uterus. The germinal stage takes around 10 days. [1] During this stage, the zygote divides in a process called cleavage.
Prenatal development (from Latin natalis 'relating to birth') involves the development of the embryo and of the fetus during a viviparous animal's gestation. Prenatal development starts with fertilization , in the germinal stage of embryonic development, and continues in fetal development until birth .
The embryo measures 13 mm (1 ⁄ 2 in) in length. Lungs begin to form. The brain continues to develop. Arms and legs have lengthened with foot and hand areas distinguishable. The hands and feet have digits, but may still be webbed. The gonadal ridge begins to be perceptible. The lymphatic system begins to develop. Main development of sex organs ...
There are three stages of fetal development. The first stage is the germinal stage begins at conception and is the shortest stage. The second stage is the embryonic stage which begins around the third week of pregnancy and ends at the eighth week. The final stage is the fetal stage which begins at the ninth week of pregnancy and lasts until birth.
Development before birth, or prenatal development (from Latin natalis 'relating to birth') is the process in which a zygote, and later an embryo, and then a fetus develops during gestation. Prenatal development starts with fertilization and the formation of the zygote , the first stage in embryonic development which continues in fetal ...
Gastrulation is the next phase of embryonic development, and involves the development of two or more layers of cells (germinal layers). Animals that form two layers (such as Cnidaria) are called diploblastic, and those that form three (most other animals, from flatworms to humans) are called triploblastic.
A fetus is a stage in the prenatal development of viviparous organisms. This stage lies between embryogenesis and birth. [1] Many vertebrates have fetal stages, ranging from most mammals to many fish. In addition, some invertebrates bear live young, including some species of onychophora [40] and many arthropods.
The second phase occurs during embryonic days 9.5 to 13.5 and causes demethylation of most remaining specific loci, including germline-specific and meiosis-specific genes. This second phase of demethylation is mediated by the TET enzymes TET1 and TET2, which carry out the first step in demethylation by converting 5-mC to 5-hydroxymethylcytosine ...