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Cells of the primordium are called primordial cells. A primordium is the simplest set of cells capable of triggering growth of the would-be organ and the initial foundation from which an organ is able to grow. In flowering plants, a floral primordium gives rise to a flower.
Sperm entry can occur anywhere in the animal hemisphere. [2] The point of sperm entry defines the dorso-ventral axis - cells opposite the region of sperm entry will eventually form the dorsal portion of the body. [1] [3] In the frog Xenopus laevis, the animal pole is heavily pigmented while the vegetal pole remains unpigmented. [4]
The egg cell is generally asymmetric, having an animal pole (future ectoderm).It is covered with protective envelopes, with different layers. The first envelope – the one in contact with the membrane of the egg – is made of glycoproteins and is known as the vitelline membrane (zona pellucida in mammals).
Size Primordial: Dormant, small, only one layer of flat granulosa cells: Primordial follicles are about 0.03–0.05 mm in diameter. Primary: Mitotic cells, cuboidal granulosa cells: Almost 0.1 mm in diameter Secondary: Presence of theca cells, multiple layers of granulosa cells: The follicle is now 0.2 mm in diameter Early tertiary
Primordial dwarfism (PD) is a form of dwarfism that results in a smaller body size in all stages of life beginning from before birth. [1] More specifically, primordial dwarfism is a diagnostic category including specific types of profoundly proportionate dwarfism, in which individuals are extremely small for their age, even as a fetus .
The embryological origin of granulosa cells remains controversial. In the 1970s, evidence emerged that the first cells to make contact with the oogonia were of mesonephric origin. It was suggested that mesonephric cells already closely associated with the oogonia proliferated throughout development to form the granulosa cell layer. [2] [3] [4]
Different forms of isogamy: A) isogamy of motile cells, B) isogamy of non-motile cells, C) conjugation (isogamy in the broad sense). Isogamy is a form of sexual reproduction that involves gametes of the same morphology (indistinguishable in shape and size), and is found in most unicellular eukaryotes. [1]
Segmentation in biology is the division of some animal and plant body plans into a linear series of repetitive segments that may or may not be interconnected to each other. This article focuses on the segmentation of animal body plans, specifically using the examples of the taxa Arthropoda, Chordata, and Annelida. These three groups form ...