Definition

Noun 1. A mass of chromatin found only in female cells: A distinct, condensed structure of chromatin (DNA and protein) that is observable in the nucleus of cells from individuals with two X chromosomes. It represents one of the two X chromosomes that is largely inactivated.

Usage

• Sex chromatin is a biological marker used to identify genetic sex at a cellular level.
• The standard test involves examining cells, often from a buccal (cheek) smear, for the presence of this structure.
• Its presence typically indicates a female genotype (XX), while its absence typically indicates a male genotype (XY).

Examples

• The presence of sex chromatin in the cell's nucleus confirmed the sample was from a female.
• Sex chromatin analysis was a common method for sex determination before more advanced genetic techniques were developed.
• The absence of sex chromatin in the amniotic fluid cells suggested the fetus was male.

Advanced Usage

• Barr body: This is a direct synonym for sex chromatin, named after the scientist Murray Barr who discovered it. The terms are often used interchangeably in genetics and cytology.
  • The report noted the presence of a Barr body, or sex chromatin, in the sampled cells.

Variants and Related Words

• Barr body (n): A synonym for sex chromatin.
• X-chromatin (n): Another less common term emphasizing its origin from an X chromosome.
• Lyonization (n): The process of X-chromosome inactivation, which creates the sex chromatin/Barr body.

Synonyms

• Barr body

Notes on Meaning

The term sex chromatin refers specifically to the inactivated X chromosome visible as a dense body. It is not a general term for all chromatin related to sex chromosomes. Its primary utility is as a diagnostic cytogenetic marker.

Noun

1. chromatin found only in female cells
   • the presence or absence of sex chromatin in cells obtained by amniocentesis makes it possible to determine the sex of a fetus