Chiasma
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- The term "Chiasma" is also sometimes used to refer to the Optic chiasm.
A chiasma (Greek χίασμα, related to the Greek letter Χ) means "crossing." In anatomy, it refers to the point where two (or more) nerves or ligaments cross or intersect. In genetics, it is a technical term for the point where two chromatids are intertwined (interwoven) in a cell.
Genetics
The chiasmata are thought to be the points where two homologous chromatids exchange genetic material during chromosomal crossover during meiosis (sister chromatids also form chiasmata between each other, but because their genetic material is identical, it does not cause any change in the resulting daughter cells). The chiasmata become visible during the diplotene stage of prophase I of meiosis I, but the actual "crossing-over" of genetic material is thought to occur during the previous pachytene stage. When each bivalent, which is composed of two pairs of sister chromatids, begin to split the only points of contact are at the chiasmata.
Chiasma frequency = 2 x recombination frequency
where recombination frequency is
recombination frequency = (No. of recombinants)/(total no. of progeny)
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Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
