Genetic Sexing System is the method of elimination of one particular sex in the population and is a kind of Sterile Insect Technique under Biological control method. The Genetic sexing system involves the elimination of one particular sex during the developmental stages which is usually females and the resulted population will have only one kind of sex preferably males. These males when released in the field mates with females thereby transferring the altered genetic material to the next generations. The subsequent generations when exposed to same conditional lethality, will again results in male population. The conditional lethal can be an Insecticide resistant gene, temperature sensitive, etc.
Genetic Sexing System is developed either by using radiation or genetic engineering technique (gene manipulations). Radiations are used to bring translocation of a particular marker like insecticide resistant gene or a phenotype marker from autosome to Y chromosome. When such individuals are treated with conditional lethal substances, for example: in case of insecticide resistant gene phenotype with insecticides, the population that lacks the insecticide resistance gene or that has insecticide susceptible gene will die leaving only the population which are insecticide resistance. In this situation, the insecticide resistance gene is linked to Y chromosome and hence the resulting population will be only males. Further the sterility increases with the number of translocations and with one translocation, it is estimated that 50% of the population will die due to abnormal genetic material. This way the insect population can be controlled very effectively. In gene manipulation technique, either the conditional lethal genes or phenotype markers are introduced as a separate plasmid or fused to the chromosomes. The system where the foreign DNA is fused with chromosome is more stable than plasmid occurrence as there is chance of loss of plasmids in subsequent generation due to cell division.
The Genetic Sexing System eliminates the critical challenge faced in the Sterile Insect Technique (SIT), where sexing of the individuals has to done before radiation, which is vary time consuming and expensive. With Genetic Sexing System, the resultant population is of only one sex, usually males which can be easily used in radiation for further procedure of SIT. With advances in genetic manipulation techniques, fluorescent markers are added for visualization aid. One sex will have fluorescent markers which make them easy to segregate and to give radiation dose.
Genetic Sexing System has been successfully developed in few insect species like Anopheles, Aedes, Mediterranean fruit fly, etc. In Anopheles albimanus, propoxur insecticide resistant gene was used as conditional lethal. A translocation involving propoxur resistance dominant allele from Chromosome 2 to Y chromosome was used for Genetic Sexing System. Further for additional check point for cross over phenomenon chromosomal inversions phenomenon was used, which acts as a suppressor of crossing over during meiosis. In such system, when lethal dose of propoxur insecticide was used for the larval population, the females which are susceptibility for propoxur insecticide dies leaving only the males that have resistant gene. This way female population is eliminated during the developmental stages resulting in the male population. Further when next generation progeny of these males with normal females treated with propoxur insecticide results once again in survival of males.
Genetic Sexing System has many advantages as it reduces the cost of mass raring procedure and time required for sexing systems in SIT. The recent advances in genetic engineering can be used in this method for higher rate of successful. Genetic Sexing System has many applications in control of mosquitoes as females are carriers of many deadly diseases including malaria, preferential elimination of females during the developmental stages will reduced the vector born diseases and also importantly the biting nuisance caused by female mosquitoes. Genetic Sexing System can also be applied in Sericulture, where male larvae give high quality and quantity silk threads than females. Genetic Sexing System utilizes control of insect pest by its own species population which is altered genetically. Hence, there is no effect on the biodiversity of the eco system. Even though there is application of insecticides in this method, the amount required will be very less when compared with traditional chemical control program. Though Genetic Sexing System is very promising, the initial phase of development is time consuming and expensive, which is a worth investing efforts. Advanced research should be aimed in developing Genetic Sexing Systems for major vectors of human diseases and also in Sericulture.
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