| egg polarity gene | A gene whose product distribution in the egg determines the anterior posterior axis of subsequent development. Best characterised in Drosophila: See: bicoid, maternal effect gene. (18 Nov 1997) |
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| segment polarity gene | <molecular biology> A segmentation gene, responsible for specifying anterior posterior polarity within individual embryonic segments. In Drosophila, there are at least 10 such genes, for example gooseberry. (18 Nov 1997) |
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| cell polarity | 1. <cell biology> In epithelial cells the differentiation of apical and basal specialisations. In many epithelia the apical and baso lateral regions of plasma membrane differ in lipid and protein composition and are isolated from one another by tight junctions. The apical membrane may, for example: be the only region where secretory vesicles fuse or have a particular ionic pumping system. 2. A motile cell must have some internal polarity in order to move in one direction at a time: a region in which protrusion will occur (the front) must be defined. Locomotory polarity may be associated with the pericentriolar microtubule organising centre and can be perturbed by drugs that interfere with microtubule dynamics. (26 Mar 1998) |
| polarity | <physics> Literally having poles (like a magnet), but used to describe cells that have one or more axes of symmetry. <cell biology> In epithelial cells, the polarity meant is between apical and baso lateral regions, in moving cells, having a distinct front and rear. Some cells seem to show multiple axes of polarity (which will hinder forward movement). (18 Nov 1997) |
| polarity of translation | Decrease in the synthesis of proteins specified by genes distal to the operator and to the site of a nonsense, frameshift, deletion or insertion mutation in an operon. A mutation which produces polarity is called a polar mutation or a polarity mutation. (12 Dec 1998) |
| neuronal polarity | Distribution of specific functions to discrete cellular domains: for example axons and dendrites that have different molecular composition, morphology and ultrastructure and perform different functions. (18 Nov 1997) |
| vitelline layer of egg | <zoology> The membrane, usually of protein fibres, immediately outside the plasmalemma of the ovum and the earlier stages of the developing embryo. Its structure and composition vary in differing animal groups. (18 Nov 1997) |
| centrolecithal egg | An egg in which the yolk is concentrated near the centre of the egg cell, as is the case in many of the insects. (05 Mar 2000) |
| microlecithal egg | An egg containing a small amount of deutoplasm. (05 Mar 2000) |
| mosaic egg | <biology> At one time a distinction was drawn between those organisms in which the egg seemed to have a firmly committed fate map built in and regulating embryos. In the former, after the first cleavage one blastomere was committed to produce one set of tissues, the other blastomere a different set and removal of one blastomere led to the production of an incomplete embryo. This was particularly obvious in mollusc development where one blastomere had the polar lobe material. This early differentiation (or determination) of blastomeres for particular fates was in distinction to regulating embryos in which the removal of one blastomere did not matter, the other blastomere compensating and producing a full set of tissues. The distinction is, however, only based upon the timing of differentiative events and within a few divisions the regulating embryo also becomes a mosaic of determined cells. (18 Nov 1997) |
| primary egg membrane | See: egg membrane. (05 Mar 2000) |
| high-egg-passage vaccine | Living Flury strain rabies virus at the 180th to 190th level egg passage (embryonate eggs), used for vaccination of cattle and cats, low-egg-passage (LEP) vaccine: at the 40th to 50th passage level, containing 103 to 104 mouse LD50; nonpathogenic in dogs but retains some pathogenicity for cattle and cats. (05 Mar 2000) |
| sea egg | <zoology> A sea urchin. Source: Websters Dictionary (01 Mar 1998) |
| secondary egg membrane | See: egg membrane. (05 Mar 2000) |
| homolecithal egg | An egg in which the total amount of yolk is small and fairly uniformly distributed throughout the cytoplasm. Synonym: isolecithal egg. (05 Mar 2000) |
| Dorset's culture egg medium | A medium for cultivating Mycobacterium tuberculosis; it consists of the whites and yolks of four fresh eggs and a solution of sodium chloride. (05 Mar 2000) |