| total cleavage | Cleavage in which the blastomeres are completely separated; the entire egg participates in cell division. Synonym: complete cleavage, total cleavage. (05 Mar 2000) |
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| enamel cleavage | The splitting of enamel in a plane parallel to the direction of the enamel rods. (05 Mar 2000) |
| equal cleavage | Cleavage producing blastomeres of like size. (05 Mar 2000) |
| equatorial cleavage | Cleavage in which the plane of cytoplasmic division is at right angles to the axis of the ovum. (05 Mar 2000) |
| yolk cleavage | Segmentation of the vitellus. (05 Mar 2000) |
| unequal cleavage | Cleavage producing blastomeres of different sizes at the two poles. (05 Mar 2000) |
| freeze cleavage | Method of specimen preparation for the electron microscope in which rapidly frozen tissue is cracked so as to produce a fracture plane through the specimen. The surface of the fracture plane is then shadowed by heavy metal vapour, strengthened by a carbon film and the underlying specimen is digested away, leaving a replica that can be picked up on a grid and examined in the transmission electron microscope. The great advantage of the method is that the fracture plane tends to pass along the centre of lipid bilayers and it is therefore possible to get en face views of membranes that reveal the pattern of Integral membrane proteins. The E face is the outer lamella of the plasma membrane viewed as if from within the cell, the P face the inner lamella viewed from outside the cell. Fracture planes also often pass along lines of weakness such as the interface between cytoplasm and membrane, so that outer and inner membrane surfaces can be viewed. Further information about the structure can be revealed by freeze etching. Extremely rapid freezing followed by deep etching has allowed the structure of the cytoplasm to be studied without the artefacts that might be introduced by fixation. (18 Nov 1997) |
| absorption lines | The dark line's in the solar spectrum due to absorption by the solar and the earth's atmosphere; the phenomenon occurs because rays passing from an incandescent body through a colder medium are absorbed by elements in that medium. (05 Mar 2000) |
| accretion lines | Line's seen in microscopic sections of the enamel, marking successive layers of added material. (05 Mar 2000) |
| amphotropic packaging cell lines | <cell culture, molecular biology> Clonal entities that express genes or act as viral vectors that infect cell lines to stably infect and then express genes of choice. Usually an amphotropic virus. (04 Nov 1997) |
| Baillarger's lines | Two laminae of white fibres that course parallel to the surface of the cerebral cortex and are visible as outer and inner line's in sections cut perpendicular to the surface; the line of Gennari in the calcarine cortex represents the outer of these lines. Synonym: Baillarger's bands. (05 Mar 2000) |
| Beau's lines | Transverse depressions on the fingernails following severe febrile disease, malnutrition, trauma, myocardial infarction, etc. (05 Mar 2000) |
| calcification lines of Retzius | Incremental line's of rhythmic deposition of successive layers of enamel matrix during development. Synonym: lines of Retzius. (05 Mar 2000) |
| Paton's lines | Concentric lines on the surface of an abnormal retina. Synonym: Paton's lines. (05 Mar 2000) |
| Voigt's lines | A dorso-ventral line of pigmentation occurring symmetrically and bilaterally for about 10 cm along the lateral edge of the biceps muscle, seen in some blacks. Synonym: Voigt's lines. (05 Mar 2000) |