Chromosomes Genetics

The evolutionary process of a genetic algorithm is accomplished by genetic operators which translate the evolutionary concepts of selection, recombination or crossover, and mutation into data processing to solve an optimization problem dynamically. Possible solutions to the problem are coded as so-called artificial chromosomes, which are changed and adapted throughout the optimization process until an optimrun solution is obtained. 

A key feature ofa genetic algorithm is that only the best chromosomes are to pass their features to the next generation during evolution. 

Selection alone cannot achieve an optimization towards the solution With mere scicction performed over a number of generations, one would get a population which comprises only the best chromosome of the original population. Therefore, an operator has to be applied which causes variance within the population, This is achieved by the application of genetic operators such as the crossover and the mutation operators. 

Crossover, which is also called recombijiation, follows the idea that aji offspring in natiu c always holds genes from both its parents. Accordingly, the genetic crossover operator takes parts of two parent chromosomes to create a new offspring. 

The chromosome in a genetic algorithm codes for the torsion angles of the rotatable bonds. 

Genetic algorithms can also be used to perform molecular docking [Judson et d. 1994 Jont et d. 1995b Oshiro et d. 1995]. Each chromosome codes not only for the internal conform tion of the ligand as described in Section 9.9.1 but also for the orientation of the ligand withi the receptor site. Both the orientation and the internal conformation will thus vary as th populations evolve. The score of each docked structure within the site acts as the fitnes function used to select the individuals for the next iteration. 

In the human cell there are 23 pairs of chromosomes containing approximately 3000 million base pairs of DNA. Short sequences of DNA, perhaps with as few as 20 nucleotide units and sometimes radiolabeled, can be obtained either by chemical synthesis (gene machine) or from cloning. These short sequences can be used to probe for a complementary sequence by looking for the position to which they bind to any DNA sample under investigation, from blood for example. Such probes can detect as little as 100 fg of DNA and are the basis of forensic genetic fingerprinting tests. 

Fig. 3. Homologous chromosomes having evenly spaced genetic markers (1 9). The segregation of the or quantitative trait loci (QTL) can be followed using marker 2. Polymorphisms within marker 2 can be used to foUow the segregation of the genes within the QTL, even though the exact location or...

Genetic Control. Manipulation of the mechanisms of inheritance of the insect pest populations has occurred most successhiUy through the mass release of steri1i2ed males, but a variety of other techniques have been studied, including the environmental use of chemostetilants and the mass introduction of deleterious mutations, eg, conditional lethals and chromosomal translocations (58 ndash 60) (see Genetic engineering). 

Colchiciae (23) is a toxic substance occurring ia Colchicum autumnale, it coataias the aucleus of pyrogaUol trimethyl ether. Colchiciae has beea used ia the treatmeat of acute gout, and ia plant genetics research to effect doubling of chromosomes. 

One method used to achieve genetic stabiUty is to insert the plasmid or the recombinant DNA direcdy into the chromosome. Since no cell can afford to lose a chromosome, this assures that the recombinant DNA is not lost as long as it remains an integral part of the chromosome. 

Figure 2 Genetic operators used to create a population of children chromosomes from a population of parent chromosomes, (a) Single-point mutation. A gene to he mutated is selected at random, and its value is modified, (b) One-point crossover. The crossover point is selected randomly, and the genes are exchanged between the two parents. Two children are created, each having genes from both parents.

Genetic damage can take place at the level of the chromosome or at the gene level. In addition, chemicals can also induce alterations in the number of chromosomes in the cells. Aneuploidy is an excess or a shortage of a single chromosome. Polyploidia is an excess of a whole set of chromosomes tn the ceil. 

Extensive research is currently underway to use biological markers (biomarkers) in exposure and risk assessment. Biomarkers include the reaction products of chemicals or their metabolic products with biological macromolecules, especially with DNA. They also involve indicators of effect, such as chromosomal damage, and indicators of individual genetic susceptibility. 

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