Chromosome exchange

Since chromosome exchanges are relatively rare events, greater biological significance should be attached to their presence than to gaps and breaks. 

Shaw MW, Cohen MM (1965) Chromosome exchanges in human leukocytes induced by mitomycin... 

Bauchinger M, Dresp J, Schmid E, et al Chromosome exchanges in lymphocytes after occupational exposure to pentachlorophenol ( CP). Mutat Res 102 83-88, 1982... 

Crossing over—In meiosis, a process in which adjacent chromosomes exchange pieces of genetic information. 

Hexavalent chromium has been shown to be a strong clastogen in experimental animals producing chromosome aberrations, sister chromosome exchanges, DNA strand breaks, oxidized base damage, DNA -DNA and DNA - protein cross-links. Human genetic studies have shown mixed results and have been limited by insufficient numbers of subjects. 

Tucker JD, Lee DA, Ramsey MJ, et al. (1994) On the frequency of chromosome exchanges in a control population measured by chromosome painting. Mutation Research 313 193-202. 

Ethanol is negative in mutagenicity assays in bacteria, mouse sperm, cell transformation in hamster and rat embryo cells, and chromosome aberrations in vitro. It produces dominant lethal effects in rats and increases sister chromosome exchange in vitro in human and nonhuman lymphocytes. 

The nerve agents are generally considered to be acute toxicants and their delayed effects have been relatively little investigated. Li et al. (1998) reported an increase in sister chromosome exchange (SCE) in the lymphocytes of victims of the Tokyo sarin disaster. Because of the probability that the victims were exposed to by-products of sarin synthesis, diisopropyl methylphospho-nate, diethyl methylphosphonate and isopropyl ethyl methylphosphonate, these were also studied. The frequency of SCE was determined in human lymphocytes exposed to these by-products all three compounds increased the frequency of SCE compared with controls. Sarin and soman... 

Wu Y, Wang X, Chen C, et al. 1998. [Serum ras P21 level and peripheral blood lymphocyte sister chromosome exchange frequency in workers exposed to coal tar pitch], Henan Yike Daxue Xuebao 33(5) 59-61. (Chinese). 

Pair up the individuals in the mating pool and generate A(> /r) new-born offspring individuals using the operators of recombination and mutation. In this study, each chromosome consists of three portions. For the first portion of the chromosome, discrete recombination operators, repeated exchange mutation operators, and evolutionary inversion mutation operators are employed. For the second portion of the chromosome, traditional gene-alter mutation operators and traditional discrete recombination operators are developed. For the third portion of the chromosome, exchange mutation operators and traditional discrete recombination operators are developed. 

K. M. Huttner and F. H. Ruddle, Study of mitomycin C-induced chromosomal exchange, Chromosoma 56, 1-13 (1976). 

S. Wolff, The kinetics for two-break chromosome exchanges, J. Theoret. Biol. 3, 304-314 (1962). 

A uniform crossover is the generalized form of crossover where chromosomal exchanges happen between parents, across multiple (the number chosen randomly) cut-points. The recombination operator has a probability associated with it which dictates how often it is used. The probability of crossover is typically set to a high value (around 99%) for binary coded representation. A random number is drawn and whenever it falls below the crossover probability, two individuals (selected using one of the selection schemes described in the previous section) are allowed to undergo crossover. If the random number test fails, the chosen individuals are duplicated and placed in the offspring population. 

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