sex chromosome

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sex chromosome

Either of a pair of chromosomes in diploid cells, or a single chromosome in haploid cells, carrying genes that determine the sex and sex-linked characteristics of an organism. Most mammals, including humans, have one pair of sex chromosomes in diploid cells, designated XX in females and XY in males.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.

sex chromosome



one of a pair of chromosomes that is different in the two sexes and is involved in SEX DETERMINATION. All remaining chromosomes in a KARYOTYPE are called AUTOSOMES. In most organisms, such as mammals and DIOECIOUS plants, the female contains two identical X-chromosomes and is the HOMOGAMETIC SEX while the male contains one X and one Y-chromosome and is the HETEROGAMETIC SEX. In birds, butterflies and moths, some fish and certain plants, the situation is reversed in the two sexes. Genes located on sex chromosomes are described as showing SEX LINKAGE.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005


One of the thread-like structures located within the cell nucleus composed of an extremely long, double-stranded DNA (deoxyribonucleic acid) helix tightly folded around proteins called histones. Each chromosome carries genes that contain the hereditary material that controls the growth and characteristics of the body. There are 46 chromosomes in each human somatic cell organized in 23 pairs, of which 22 pairs are similar in appearance but differ at the molecular level. They are called autosomal chromosomes or autosomes and are designated by a number (with chromosome 1 being the longest, followed by chromosome 2, etc.). The other pair, the sex chromosomes determines the sex of the individual. In mammals the two sex chromosomes of females are alike (homologous) and are referred to as X chromosomes. Males carry one X chromosome along with a much shorter chromosome, the Y chromosome. Each chromosome has a centromere that divides it into two arms, the short arm 'p' and the long arm 'q'. Disorders of chromosome number in which the number of chromosomes is above or below the normal (46) are called aneuploidy. Common forms of aneuploidy are trisomy in which there is one extra chromosome and monosomy in which there is one less, than the normal 46. They rarely cause specific eye diseases but affected individuals present ocular manifestations. Examples: Down's syndrome (trisomy of chromosome 21), Edwards' syndrome (trisomy 18), Turner's syndrome (monosomy 45 XO). There are other chromosome abnormalities such as translocation (one segment of a chromosome is transferred to another chromosome) as may occur in congenital anterior polar cataract, deletion (a loss of a piece of chromosome) as in aniridia, choroideremia, retinoblastoma, etc. Other cases involve damage of a chromosome (e.g. fragile X syndrome). See defective colour vision; gene; mitosis; mutation.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann
References in periodicals archive ?
Graves, "Relationships between vertebrate ZW and XY sex chromosome systems," Current Biology, vol.
(6) Interestingly, Stella Welsh was discovered to have ambiguous genitalia and abnormal sex chromosomes during an autopsy after she was a victim of a shooting incident in 1980, (6) highlighting that sex verification during sporting events would not only identify those cheating but also athletes with a rare intersex condition.
In males, only autosomes were recognized, whereas sex chromosomes had a diffused structure (Fig.
The standard way of making reference to an individual's karyotype is to note the total number of chromosomes followed by the type of sex chromosomes. For example, normal human males have the 46, XY karyotype, whereas normal human females have the 46, XX karyotype.
Although White's interests covered many aspects of chromosome biology, he made relevant contributions to sex chromosome mechanisms and the evolution of sex chromosomes (White 1940a, b; 1941a,b).
Conclusions: Among embryos with a clear diagnosis of sex chromosome, about one-fifth showed abnormal signals.
In the purest sense of the term, a sex-linked trait is simply one that is carried on a gene attached, or linked, to either the male or the female sex chromosome.
The disorders of sex development are now broadly grouped into three main diagnostic categories namely 46 XY DSD (previously called male Pseudo hermaphroditism), 46 XX DSD (previously called female Pseudo hermaphroditism) and sex chromosome DSD (previously called true hermaphroditism).
A multiple sex chromosome system of the X1X20 type is the most common in spiders (i.e., Suzuki, 1954) but is rare in other animal groups.
Evolution of the karyotype and sex chromosome systems in basal clades of araneomorph spiders (Araneae: Araneomorphae).