Pronunciation: [t͡ʃˈa͡ɪəzmə] (IPA) 
The word "chiasma" is sometimes spelled with an "x" instead of a "ch". However, the correct spelling is with a "ch", as in "kai-az-muh". The reason for this spelling is because the word comes from the Greek word "khiasma". The "ch" sound in Greek is represented by the letter "chi", which in turn has been changed to "ch" in the Roman alphabet. Therefore, the correct and more phonetically accurate spelling of this word is "chiasma".
Chiasma is a noun derived from the Greek word khiasma, which means "crossing." It refers to a biological structure or phenomenon found in various organisms, particularly in genetics and neurobiology.
In genetics, a chiasma is a point at which two homologous chromosomes exchange genetic material during meiosis, the process of cellular division that produces sex cells. This exchange of genetic material between the chromosomes gives rise to genetic recombination or crossover, contributing to genetic diversity and variation in offspring. The chiasma is formed when segments of non-sister chromatids break and reconnect with the corresponding segments of the other homologous chromosome. This process facilitates the exchange of alleles, which are alternative forms of a gene, resulting in newly combined genetic variations.
In neurobiology, chiasma refers to a specific anatomical structure in the brain. The optic chiasm, for instance, is a region located at the base of the brain where the optic nerves partially cross over. This crossover allows for the integration of visual information received by both eyes, contributing to binocular vision. Other examples include the sensory and motor nerve fibers crossing over in the medulla oblongata to control movement and sensation on opposite sides of the body.
In both cases, the term chiasma signifies a point of crossing and interchange, either between chromosomes during genetic recombination or nerve fibers in the nervous system.
Chiasm.
A practical medical dictionary. By Stedman, Thomas Lathrop. Published 1920.
In anat., the central body of nervous matter formed by the junction and the crossing of the fibres of the optic nerves.
Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874.
The word "chiasma" has its roots in ancient Greek. It is derived from the Greek word "khíasma" (χίασμα), which means "crossing". The term was first introduced in the late 19th century by German anatomist Wilhelm Waldeyer, who used it to describe the cross-shaped appearance of certain structures, such as the optic chiasm in the brain. In biology, chiasma refers to the point where two chromosomes cross over during meiosis, exchanging genetic material.
