| Z chromosome | <genetics> This is a sex chromosome in certain animals such as chickens and moths. In the Z chromosome karyotype, females are heterogametic, so males are ZZ and females are WZ. (11 May 1997) |
|---|---|
| unpaired chromosome | A chromosome existing without its normal homologous chromosome; at the reduction division of gametogenesis an accessory chromosome is likely to be included in one daughter cell and not in the other, but may be lost completely by lagging behind on the equatorial plate. Synonym: monosome, odd chromosome, unpaired allosome, unpaired chromosome. (05 Mar 2000) |
| lampbrush chromosome | <cell biology> Large chromosomes (as long as 1mm), actually meiotic bivalents, seen during prophase of the extended meiosis in the oocytes of some Amphibia. Segments of DNA form loops in pairs along the sides of the sister chromosomes, giving them a brush like appearance. These loops are not permanent structures but are formed by the unwinding of chromomeres and represent sites of very active RNA synthesis. (27 Jun 1999) |
| late replicating chromosome | A chromosome (often anomalous) that is shown, e.g., by incorporation of a labelled nucleotide, to undergo delayed duplication preliminary to mitosis; formerly used as a means of distinguishing members of a group of chromosome's. (05 Mar 2000) |
| fragile x chromosome | X chromosome with a fragile site associated with a frequent form of mental retardation. The fragile X chromosome was first sighted by Herbert A. Lubs in 1969. The fragile X is also called FRAXA (the second A signifies it was the first FRAgile site found on the X chromosome). It is due a trinucleotide repeat (a recurring motif of 3 bases) in the DNA at that spot. (12 Dec 1998) |
| abdominal ring | The opening in the transversalis fascia through which the ductus deferens (or round ligament in the female) and gonadal vessels enter the inguinal canal. Located midway between anterior superior iliac spine and pubic tubercle, it is bounded medially by the lateral umbilical ligament (inferior epigastric vessels) and inferiorly by the inguinal ligament. Indirect inguinal hernias exit the abdominal cavity via the deep inguinal ring Synonym: annulus inguinalis profundus, abdominal ring, annulus abdominalis, internal inguinal ring. (05 Mar 2000) |
| amnion ring | The ring formed by the attachment of the amnion to the umbilical cord at its point of emergence from the umbilicus. (05 Mar 2000) |
| annuloplasty ring | The dilated annulus is sutured, often to a prosthetic ring, thereby reducing it to its normal systolic size. (05 Mar 2000) |
| anterior limiting ring | The periphery of the cornea marking the termination of Descemet's membrane and the anterior border of the trabecular meshwork; an important landmark in gonioscopy. Synonym: Schwalbe's ring. (05 Mar 2000) |
| Balbani ring | An extremely large puff at a band of a polytene chromosome. (05 Mar 2000) |
| Balbiani ring | <cell biology, genetics> The largest puffs seen on the polytene chromosomes of Diptera are called Balbiani rings after the nineteenth century microscopist who first described polytene chromosomes. (18 Nov 1997) |
| Bandl's ring | A constriction located at the junction of the thinned lower uterine segment with the thick retracted upper uterine segment, resulting from obstructed labour; this is one of the classic signs of threatened rupture of the uterus. Synonym: Bandl's ring, Baudelocque's uterine circle, Scanzoni's second os. (05 Mar 2000) |
| benzene ring | The closed-chain arrangement of the carbon and hydrogen atoms in the benzene molecule. See: cyclic compound. (05 Mar 2000) |
| Bickel's ring | The broken ring of lymphoid tissue, formed of the lingual, faucial, and pharyngeal tonsils. Synonym: Bickel's ring, tonsillar ring, Waldeyer's throat ring. (05 Mar 2000) |
| Cabot's ring bodies | Ring-shaped or figure-of-eight structures that stain red with Wright's stain, found in red blood cells in severe anaemias, possibly a remnant of the nuclear membrane; a form of basophilic degenerative process. (05 Mar 2000) |