![]() ![]() b) -catenin, which has become localized to the nucleus in the Nieuwkoop center as a result of cortical rotation, turns on high levels of the TGF- signalling molecule, Nodal, and this relatively high level distinguishes. So, the correct answer is 'Dorsal lip of the blastopore'. a) The cells of the Spemann organizer become different as they pass over the dorsal lip of the blastopore during gastrulation. Hans Spemann and Hilde Mangold experiments proved that the dorsal lip of blastopore makes the neural tubes, cartilaginous skeletons, mesoderm etc and therefore called as the Specman's primary organizer. The Primary Organizer has a dorsalizing effect, and together with the Sperm Entry Point (SEP) gives rise to the dorsal/ventral axis. It gives rise to the Primary Organizer, which is the dorsal lip of the blastopore (DLB). In embryology, an organizer is the morphogenetic effect caused by one organic tissue which produces a chemical molecule that affects another part of the embryo to form a part which otherwise would not have produced. The Nieuwkoop Center is the dorsal- and vegetal-most cell of the early blastula. The research by Hans Spemann (German embryologist) and his colleague Hilde Mangold did a transplantation experiment in frogs which led to the discovery of organizers. However, whereas the amphibian dorsal blastopore lip is thought to form a notochord anteriorly by animalward migration on the inner surface of the blastocoel roof, the chick Hensen’s node migrates and forms a notochord posteriorly. In the development of a frog embryo, the dorsal lip of the blastopore would be the spearman’s primary organizer. Therefore, these tissues are considered the equivalent structure, termed the organizer. The newly formed zygote later goes through the mitotic divisions and forms a multicellular embryo. The embryogenesis starts with the fusion of the egg cell and sperm cell and gets fertilized, from which a zygote (diploid) is developed. Hint: The process of formation and development of an embryo is known as embryogenesis. ![]()
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