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ShareIn organisms that reproduce sexually, once a sperm fertilizes an egg cell, the result is a cell called the zygote that has all the DNA of two parents.
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In plants, animals, and some protists, the zygote will begin to divide by mitosis to produce a multicellular organism. In animals, the development of the zygote into an embryo proceeds through specific recognizable stages of blastula, gastrula, and organogenesis.
The blastula stage typically features a fluid-filled cavity, the blastocoel, surrounded by a sphere or sheet of cells, also called blastomeres. During gastrulation the cells of the blastula undergo coordinated processes of cell division, invasion, and/or migration to form two (diploblastic) or three (triploblastic) tissue layers.
In triploblastic organisms, the three germ layers are called endoderm, ectoderm and mesoderm.
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.
For more information about the topic Embryo, read the full article at Wikipedia.org, or see the following related articles:
Fertilisation — Fertilisation, also spelt fertilization (also known as conception, fecundation and syngamy), is fusion of gametes to form a new organism of the same ... > read more
Mammalian embryogenesis — Mammalian embryogenesis is the process of cell division and cellular differentiation which leads to the development of a mammalian embryo. A mammal ... > read more
Germ layer — A germ layer is a collection of cells, formed during animal embryogenesis. Germ layers are only really pronounced in the vertebrates. However, all ... > read more
Biological life cycle — A life cycle is a period involving one generation of an organism through means of reproduction, whether through asexual reproduction or sexual ... > read more
Morphogenesis — Morphogenesis is one of three fundamental aspects of developmental biology along with the control of cell growth and cellular differentiation. ... > read more
Neural development — The study of neural development draws on both neuroscience and developmental biology to describe the cellular and molecular mechanisms by which ... > read more
Umbilical cord — In placental mammals, the umbilical cord is a tube that connects a developing embryo or fetus to its placenta. It contains one or two major vessels, ... > read moreEditor's Note: This article is not intended to provide medical advice, diagnosis or treatment.
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