- sex chromosome
a chromosome, differing in shape or function from other chromosomes, that determines the sex of an individual.[1910-15]
* * *Either of a pair of chromosomes that determine whether an individual is male or female.The sex chromosomes of mammals are designated X and Y; in humans, they constitute one pair of the total 23 pairs of chromosomes. Individuals possessing two X chromosomes (XX) are female; those having one X and one Y chromosome (XY) are male. The X chromosome is larger and carries more genetic information than the Y. Traits controlled only by genes found on the X chromosome (e.g., hemophilia, red-green colour blindness) are said to be sex-linked. Sex-linked traits occur far more frequently in males than in females, since a male inheriting an allele for a recessive (see recessiveness) trait on the X chromosome lacks a corresponding allele on the Y chromosome that might counteract its effects. Several disorders are associated with an abnormal number of sex chromosomes, including Turner syndrome and Klinefelter syndrome.
* * *▪ geneticseither of a pair of chromosomes that determine whether an individual is male or female. The sex chromosomes of human beings and other mammals are designated by scientists as X and Y. In humans the sex chromosomes comprise one pair of the total of 23 pairs of chromosomes. The other 22 pairs of chromosomes are called autosomes.Individuals having two X chromosomes (XX) are female; individuals having one X chromosome and one Y chromosome (XY) are male. The X chromosome resembles a large autosomal chromosome with a long and a short arm. The Y chromosome has one long arm and a very short second arm. This path to maleness or femaleness originates at the moment of meiosis, when a cell divides to produce gametes (gamete), or sex cells having half the normal number of chromosomes. During meiosis the male XY sex-chromosome pair separates and passes on an X or a Y to separate gametes; the result is that one-half of the gametes (sperm) that are formed contains the X chromosome and the other half contains the Y chromosome. The female has two X chromosomes, and all female egg cells normally carry a single X. The eggs fertilized by X-bearing sperm become females (XX), whereas those fertilized by Y-bearing sperm become males (XY).Unlike the paired autosomes, in which each member normally carries alleles (allele) (forms) of the same genes, the paired sex chromosomes do not carry an identical complement of genetic information. The X chromosome, being larger, carries many more genes than does the Y. Traits controlled by genes found only on the X chromosome are said to be sex-linked (see linkage group). Recessive sex-linked traits, such as hemophilia and red–green colour blindness, occur far more frequently in men than in women. This is because the male who inherits the recessive allele on his X chromosome has no allele on his Y chromosome to counteract its effects. The female, on the other hand, must inherit the recessive allele on both of her X chromosomes in order to fully display the trait. A woman who inherits the recessive allele for a sex-linked disorder on one of her X chromosomes may, however, show a limited expression of the trait. The reason for this is that, in each somatic cell of a normal female, one of the X chromosomes is randomly deactivated. This deactivated X chromosome can be seen as a small, dark-staining structure—the Barr body—in the cell nucleus.The effects of genes carried only on the Y chromosome are, of course, expressed only in males. Most of these genes are the so-called maleness determiners, which are necessary for development of the testes in the fetus.Several disorders are known to be associated with abnormal numbers of sex chromosomes. Turner's syndrome and Klinefelter's syndrome (qq.v.) are among the most common of these. See also X trisomy (X-trisomy); XYY-trisomy.
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sex chromosome — n a chromosome (as the X chromosome or the Y chromosome in humans) of a sexually reproducing eukaryotic organism that is directly concerned with the inheritance of sex, that contains the genes governing the inheritance of various sex linked and… … Medical dictionary
sex chromosome — n. a sex determining chromosome in the germ cells of most animals and a few plants: in most animals, including human beings, all the eggs carry an X chromosome and the spermatozoa either an X or Y chromosome, and an egg receiving an X chromosome… … English World dictionary
sex chromosome — 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). In birds, the opposite is the case, the male being XX and… … Dictionary of molecular biology
sex chromosome — ► NOUN ▪ a chromosome concerned in determining the sex of an organism (in mammals the X and Y chromosomes) … English terms dictionary
sex chromosome — sex chromosome. См. половая хромосома. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) … Молекулярная биология и генетика. Толковый словарь.
sex chromosome — noun (genetics) a chromosome that determines the sex of an individual mammals normally have two sex chromosomes • Topics: ↑genetics, ↑genetic science • Hypernyms: ↑chromosome • Hyponyms … Useful english dictionary
sex chromosome — UK / US noun [countable] Word forms sex chromosome : singular sex chromosome plural sex chromosomes biology a chromosome that controls what the sex of a living thing will be, for example the x chromosomes and y chromosomes in humans and animals … English dictionary
sex chromosome — Differentiated chromosome which is responsible for the determination of sex of the individual. For all mammals, a small number of flowering plants and many insects, female individuals carry a pair of X chromosomes, and males carry one X and one Y … Glossary of Biotechnology
sex chromosome — sex′ chro mosome n. gen a chromosome that determines the sex of an individual … From formal English to slang
sex chromosome — chromosome that determines the sex of a creature … English contemporary dictionary