| hybrid sterility | <genetics, zoology> The inability of a hybrid to produce viable offspring. Whether an animal hybrid is sterile or fertile depends mainly on how closely its two parent species are related. For example: mules (which are hybrids between male donkeys and female horses) are usually sterile, while hybrids between domestic dogs and wolves are fertile (hybrids between wolves and foxes are also fertile, but hybrids between dogs and foxes are sterile). (09 Oct 1997) |
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| hybrid swarm | A group of morphologically distinctive individuals which results from the creation of hybrids between two parent species, then the backcrossing of the offspring to members of the parent species and the interbreeding among the hybrid individuals. (09 Oct 1997) |
| hybrid vigor | The adaptive superiority of heterozygous genotypes with respect to one or more characters in comparison with the corresponding homozygotes. (12 Dec 1998) |
| somatic hybrid | Heterokaryon formed between two somatic cells, usually from different species. See: somatic cell genetics. (18 Nov 1997) |
| SV40-adenovirus hybrid | A virion consisting of SV40 genetic material encased in an adenovirus capsid. (05 Mar 2000) |
| DNA-RNA hybrid | Double-stranded polynucleic acids in which one strand is DNA and the other strand is the complementary RNA; formed during transcription and during multiplication of oncogenic RNA viruses. (05 Mar 2000) |
| upper hybrid waves | <radiobiology> Similar to lower hybrid waves, but at a higher frequency. Not truly propagating waves, but plasma oscillations. (09 Oct 1997) |
| fusion-fission hybrid | <radiobiology> Proposed nuclear reactor relying on both fusion and fission reactions. A central fusion chamber would produce neutrons to induce fission in a surrounding blanket of fissionable material. The neutron source could also be used to convert other materials into additional fissile fuels (breeder hybrid). Safer than a plain fission reactor because the fission fuel relies on the fusion neutrons, and therefore cannot achieve criticality. On the other hand, hybrids are more complex because of the fusion power core, and still generate fission's radioactive byproducts. But a fusion-fission hybrid could be more economical and have less stringent technical requirements than a pure fusion reactor. (05 Jan 1998) |
| lower hybrid waves | <physics> Electrostatic ion oscillations at a frequency intermediate to the electron extraordinary wave (high frequency) and the magnetosonic wave (low frequency). (09 Oct 1997) |
| amphoric resonance | A percussion sound, like that produced by striking a large empty bottle, obtained by percussing over a pulmonary cavity. Synonym: cavernous resonance. (05 Mar 2000) |
| bandbox resonance | A peculiar, partly tympanitic, partly vesicular sound, obtained on percussion in cases of pulmonary emphysema. Synonym: bandbox resonance, wooden resonance. (05 Mar 2000) |
| bellmetal resonance | In cases of a large pulmonary cavity or of pneumothorax, a clear metallic sound obtained by striking a coin, held against the chest, by another coin, or by flicking the chest wall with one's fingernail; the sound is heard on auscultating the chest wall on the same side anteroposteriorly. Synonym: anvil sound, bell sound, coin test. (05 Mar 2000) |
| magnetic resonance angiography | Non-invasive method of vascular imaging and determination of internal anatomy without injection of contrast media or radiation exposure. The technique is used especially in cerebral angiography as well as for studies of other vascular structures. (12 Dec 1998) |
| Magnetic Resonance Imaging | A special imaging technique used to image internal stuctures of the body, particularly the soft tissues. An MRI image is often superior to a normal X-ray image. It uses the influence of a large magnet to polarize hydrogen atoms in the tissues and then monitors the summation of the spinning energies within living cells. Images are very clear and are particularly good for soft tissue, brain and spinal cord, joints and abdomen. These scans may be used for detecting some cancers or for following their progress. Acronym: MRI (11 Nov 1997) |
| magnetic resonance imaging, cine | A type of imaging technique used primarily in the field of cardiology. By coordinating the fast gradient-echo mri sequence with retrospective ecg-gating, numerous short time frames evenly spaced in the cardiac cycle are produced. These images are laced together in a cinematic display so that wall motion of the ventricles, valve motion, and blood flow patterns in the heart and great vessels can be visualised. (12 Dec 1998) |