| sex chromosome | <genetics> Chromosome that determines the sex of an animal. In humans, where the two sex chromosomes (X and Y) are dissimilar, the female has two X chromosomes and the male is heterogametic (XY). <zoology> In birds, the opposite is the case, the male being XX and the female XY, in many organisms, there is only one sex chromosome and one sex is XX, the other X0. A portion of the X and Y chromosomes is similar and is known as the pseudoautosomal region. (14 Oct 1997) |
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| sex chromosome imbalance | Any abnormal pattern of sex chromosomes; e.g., XXY in men with seminiferous tubule dysgenesis, XO in women with Turner's syndrome; rarer patterns of imbalance are XXX, XXXY, and XYY. See: isochromosome. (05 Mar 2000) |
| submetacentric chromosome | A chromosome with the centromere so placed that it divides the chromosome into two arms of strikingly unequal length. (05 Mar 2000) |
| nucleolar chromosome | A chromosome regularly associated with a nucleolus. (05 Mar 2000) |
| derivative chromosome | An anomalous chromosome generated by translocation. Synonym: translocation chromosome. (05 Mar 2000) |
| dicentric chromosome | <cell biology> A chromosome with two centromeres instead of the normal one. Such an oddity can form if chromosomes break and then the fragments re-fuse with one another in a different combination than before they broke. (09 Oct 1997) |
| quinacrine chromosome banding stain | q-banding stain |
| odd 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) |
| telocentric chromosome | <genetics> Chromosome with the centromere located at one end. (18 Nov 1997) |
| translocation chromosome | An anomalous chromosome generated by translocation. Synonym: translocation chromosome. (05 Mar 2000) |
| Y chromosome | <genetics> The small chromosome that is male-determining in most mammal species and found only in the heterogametic sex. Thus in mammals the male has one Y chromosome and one X chromosome. One region of the Y chromosome, the pseudoautosomal region, is homologous to and pairs with the X chromosome. The primary determinant of male sexual development is found on the unpaired, differentiated segment of the Y chromosome. It carries few other genes besides those dictating sperm development and triggering appropriate hormonal output. (18 Nov 1997) |
| yeast artificial chromosome | <molecular biology> A vector system that allows extremely large segments of DNA to be cloned. Useful in chromosome mapping, contiguous yeast artificial chromosomes covering the whole Drosophila genome and certain human chromosomes are available. Acronym: YAC (15 Nov 1997) |
| 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) |