sex chromatin

chromatin /chro·ma·tin/ (kro´mah-tin) the substance of chromosomes, the portion of the cell nucleus that stains with basic dyes. See euchromatin and heterochromatin.

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sex chromatin  Barr body; the persistent mass of the inactivated X chromosome in cells of normal females.

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sex chromatin

n.

See Barr body.

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sex chromatin,

a densely staining mass within the nucleus of all nondividing cells of normal mammalian females. It represents the heterochromatin of the inactivated X chromosome. Examination of cells obtained by amniocentesis for the presence of sex chromatin is a technique used for determining the sex of a baby before birth. Sex chromatin is also found as a drumstick-shaped mass attached to one of the nuclear lobes in polymorphonuclear leukocytes in normal females. Also called Barr body. See also Lyon hypothesis.

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chromatin

the substance of the chromosomes, composed of nucleic acids and basic proteins (histones), the material in the nucleus that stains with basic dyes.

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sex chromatin

Barr body; the persistent mass of the material of the inactivated X chromosome in cells of normal females. See also drumstick.

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sex

1. the fundamental distinction, found in most species of animals and plants, based on the type of gametes produced by the individual or the category to which the individual fits on the basis of that criterion. Ova, or macrogametes, are produced by the female, and spermatozoa, or microgametes, are produced by the male. The union of these distinctive germ cells results in the production of a new individual in sexual reproduction.

2. to determine the sex of an animal.

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sex cell

see germ cell, gamete.

sex chromatin

the persistent mass of chromatin situated at the periphery of the nucleus in cells of normal females; it is the material of the inactivated sex chromosome. Called also Barr body.

chromosomal sex

sex as determined by the presence of the XX (female) or the XY (male) genotype in somatic cells, without regard to phenotypic manifestations. Called also genetic sex.

sex chromosomes

see sex chromosomes.

sex determination

1. the change in the fetus to a male or female configuration; the process by which the sex of an organism is fixed, associated, in animals, with the presence or absence of the Y chromosome.

2. diagnosis of the sex of the fetus before birth performed by examination of fetal fluids obtained by amniocentesis.

sex determining region of Y

a single gene responsible for determining the sex of an animal.

sex drive

see libido.

endocrinological sex

the phenotypic manifestations of sex determined by endocrine influences, such as mammary development, etc.

genetic sex

chromosomal sex.

sex glands

in the male includes the prostate, seminal vesicles, ampullae and bulbourethral glands; in the female includes ovaries.

gonadal sex

the sex as determined on the basis of the gonadal tissue present (ovarian or testicular).

sex hormones

glandular secretions involved in the regulation of sexual functions. The principal sex hormone in the male is testosterone, produced by the testes. In the female the principal sex hormones are the estrogens and progesterone, produced by the ovaries.

These hormones influence the secondary sex characters, such as the shape and contour of the body and head, mammary development and the pitch of the voice. The male hormones stimulate production of spermatozoa, and the female hormones control ovulation, pregnancy and the estral cycle.

sex-linkage

includes X-linked (much the most common) and Y-linked loci.

sex-linked inheritance

see sex-linkage (above).

morphological sex

sex determined on the basis of the morphology of the external genitals.

neutrophil sex lobe

see drumstick lobe.

nuclear sex

the sex as determined on the basis of the presence or absence of sex chromatin in somatic cells, its presence normally indicating the XX (female) genotype, and its absence the XY (male) genotype.

sex parity

see sex ratio (below).

sex pheromone

see pheromone.

sex ratio

proportion of female to male births.

sex reversal

the sexual condition of animals in which gonadal sex and chromosomal sex are dissimilar.

sex steroids

steroidal compounds acting as hormones in reproductive processes; the principal ones are estrogen, progesterone, testosterone.