Development of Caenorhabditis elegans

The nematode worm Caenorhabditis elegans is a small (1 mm long), unsegmented, vermiform, free-living soil nematode. It is a relatively simple, and precisely structured organism, extensively used as a model organism for molecular and developmental biology. The body of an adult C. elegans hermaphrodite contains exactly 959 somatic cells, whose entire lineage has been traced through its transparent cuticle. Its genome has …

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Blastocyst- Stages, Significance

The preimplantation period of human embryo development is remarkable and characterized by successive changes in terms of genetic control, physiology, and morphology of the embryo. Blastocyst (Greek, blastos= sprout + cystos = cavity) is a distinctive stage of mammalian embryo development, characterized by a hollow cellular mass that forms in early development. It is an embryo that has developed for five to six days after …

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DNA Methylation

DNA methylation is a process by which methyl groups are added to the DNA molecule. It is an epigenetic mechanism that occurs by the addition of a methyl (-CH3) group to DNA, thereby often modifying the function of the genes and affecting gene expression.  The most widely characterized DNA methylation process is the covalent addition of the methyl group at the 5-carbon of the cytosine ring resulting in …

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Human Embryo Transfer

Human Embryo Transfer

‘Embryo transfer’ refers to the transplantation of a mammalian preimplantation embryo into the reproductive tract of a recipient female so that it may implant and continue to develop to birth. Mammalian embryos of many species can develop in vitro from fertilization to the blastocyst stage (approximately 100 cells), but at this point, they must implant in the uterus in order for embryogenesis …

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Human Embryogenesis

Human embryogenesis refers to the development and formation of the human embryo. It encompasses the first eight weeks of development after fertilization, in which a single cell formed at fertilization turns into an organism with a multi-level body plan. It is characterized by the process of cell division and cellular differentiation that occurs during the early stages of development. The entire process of embryogenesis …

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Gastrulation- Process, Consequences

The most characteristic event occurring during the third week of gestation is gastrulation. Gastrulation is a formative process by which the three germ layers, which are precursors of all embryonic tissues, and the axial orientation are established in embryos. During gastrulation, the bilaminar embryonic disc is converted into a trilaminar embryonic disc. Extensive cell shape changes, rearrangement, movement, and alterations …

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Comparative Embryology- Principle, Significance

Comparative embryology is the branch of embryology that compares and contrasts embryos of different species, showing how all animals are related. Put simply, comparative embryology is the comparison of embryo development across species. All vertebrate embryos follow a common developmental path due to their common ancestry. They pass from single cells to multi-celled zygotes, clumps of cells called morulas, and hollow balls of cells called blastulas, …

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Epiblast- Development and Significance

Epiblast- Development, and Significance As implantation of the blastocyst occurs, morphologic changes in the embryoblast produce a bilaminar embryonic disc composed of epiblast and hypoblast cells. Epiblast is derived from the inner cell mass and lies above the hypoblast.  The epiblast is thus, one of the two distinct layers arising from the inner cell mass in the mammalian blastocyst. It …

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Morula- Stage, Development, Significance

Within twenty-four hours after fertilization, the zygote initiates a rapid series of mitotic cell divisions called cleavage. These divisions are not accompanied by cell growth, so they subdivide the large zygote into many smaller daughter cells called blastomeres. The first cleavage division divides the zygote to produce two daughter cells. The second division, which is complete at about forty hours …

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The Prenatal Developmental Period

The human body, like that of most animals, develops from a single cell produced by the union of a male and a female gamete (or sex cell).  Cell division, cell migration, programmed cell death (apoptosis), differentiation, growth, and cell rearrangement transform the fertilized oocyte, a highly specialized, totipotent cell, a zygote, into a multicellular human being. It is customary to divide human development into prenatal …

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