Genes Exchanged

Advanced virology. RNA viruses and retrotransposons predated the formation of DNA vimses in the pre-cellular virus world of Koonin et al [18]. Precellular ribosome-like entities might have been operated by ribozymes and RNPs. Cellular ribosomes could remain operational extracellularly (Heinrich Matthaei and Marshall Nirenberg, vide infra). In the cellular world, there are two enzymes that transcribe RNA to DNA telomerase and reverse transcriptase (RT). The gene of the enzyme RT is a component of the retroviral genome [32]. Template-encoded proteins of this complexity are not expected to have been formed in the pre-cellular era, unless precellular RNP-armed entities resembling ribosomes existed. 

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VIII. Mammalian-D/wop/iifa Homeobox Gene Exchanges.105... 

VIII. MAMMALIAN-DROSOPHILA HOMEOBOX GENE EXCHANGES... 

Aravind, L., Tatusov, R. L., Wolf, Y. I., Walker, D. R., and Koonin, E. V. (1998c). Evidence for massive gene exchange between archaeal and bacterial hyperthermophiles. Trends Genet. 14, 442-444. 

Higher rates of horizontal gene exchange, based on the abundant presence of plasmid transfer (Tra), plasmid mobilization (Mob), transposons (Tn), insertion seqnences (IS), and similar fnnctions or elements, seem to be a rule in these variable gene pools. 

Two processes are involved in speciation. Firstly, the two populations must evolve sufficient ecological differences that they do not suffer from competitive exclusion. In the case of metal-tolerant ecotypes, this condition has been fulfilled. Secondly, they must evolve sufficient barriers to gene exchange that the two gene pools are effectively isolated, and will evolve independently. There are a number of ways in which this could occur, and the first stages of this have been observed in a number of studies of metal-tolerant plants. 

Howell, M. J. (1985). Gene exchange between hosts and parasites. International Journal for Parasitology, 15 597-600. 

Made, I.,Rayssiguier, C., andRadman, M. (1995). Interspecies gene exchange in bacteria the role of SOS and mismatch repair systems in evolution of species. Cell, 80, 507-515. 

The behavior of hybrid plants and their descendants will depend on seed viability, predation and germintion, plant survival from herbicide or crop competition, fertility, and gene exchanges within the weed population. Preliminary estimates lead us to think that the risk of having resistant weeds is not acceptable. Therefore, it is necessary to start a breeding program to produce a tetraploid resistant foxtail millet that reduces the chance of having viable hybrids between the crop and the weed. 

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