chiasma
/kai'æzmə/
Definition
- Noun:
- An anatomical crossing point: A chiasma is a point where two structures, particularly nerve tracts or chromosomes, cross each other in an X-shaped formation.
- A genetic crossover site: In genetics, a chiasma is the visible point of contact between paired homologous chromosomes during meiosis, where crossing over and exchange of genetic material occurs.
Usage and Examples
- Noun (Anatomical):
- The optic chiasma is where the optic nerves from each eye partially cross.
- A surgical procedure must carefully avoid damaging the chiasma of the nerve tracts.
- Noun (Genetic):
- The formation of a chiasma is essential for genetic recombination.
- Under the microscope, we could observe a chiasma between the paired chromosomes.
Advanced Usage
- "Chiasma formation": The process by which homologous chromosomes become linked at a crossover point during meiosis.
- Chiasma formation is a prerequisite for proper chromosome segregation.
- "Chiasma frequency": The average number of chiasmata observed per cell during meiosis, often used as a measure of genetic recombination.
- The chiasma frequency varies between different species and chromosomal regions.
Variants and Related Words
- Chiasm (n): An alternative, often synonymous, term for chiasma, especially in anatomical contexts.
- The term 'optic chiasm' is more common than 'optic chiasma' in many textbooks.
- Chiasmal (adj): Pertaining to or of the nature of a chiasma.
- The chiasmal region showed signs of inflammation.
- Chiasmatic (adj): Relating to a chiasma.
- The chiasmatic cistern is a space in the brain near the optic chiasm.
Synonyms
- Crossing: A point where two things intersect (general term).
- Decussation: A technical term for an X-shaped crossing, especially of nerve fibers.
- Crossover: The point or process of exchange, particularly in genetics.
Related Terms and Concepts
- Synapsis: The pairing of homologous chromosomes, which precedes chiasma formation.
- Crossing over: The exchange of genetic material that occurs at a chiasma.
- Bivalent: The structure formed by a pair of homologous chromosomes held together by a chiasma.
Noun
-
an intersection or crossing of two tracts in the form of the letter X
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