Plant biology Essay Example | Topics and Well Written Essays - 1250 words

Plant biology - Essay Example HGT is observed mainly between prokaryotes (single-celled organisms) like bacteria but also can be in Eukaryotes (protists, fungi, plants, animals, humans) to a lesser extent. HGT was first described by Ochiai et al. in 1959, in relation to transfer of antibiotic resistance between different bacterial species. Thereafter many scientists have studied and discussed about this phenomenon and now it is accepted that HGT is not a rare event and what is present in the biological world today is not a result of vertical gene transmission alone but also of HGT. Biological kingdom of earth can be categorized into three domains as bacteria, archea and eukaryotes. During vertical gene transmission, genetic information exchange between members of these domains is restricted to closely-related organisms with homologous DNA sequences. Therefore the ancestry of an organism could be traced back by analyzing their DNA and individuals with similar gene sequences can be grouped together to construct the evolutionary pathway. However, as HGT can transfer genes across wide phylogenetic distances, this picture become obscure. The phylogenetic tree of life (Figure 1) which present the relationship among different biological taxa is thus complicated by HGT as numerous interconnecting branches became obvious due to the presence of homologous DNA sequences in distantly-related organisms (Simonson et al.). Transfer of genes between different biological kingdoms, such as between eucaryotes and bacteria, or between bacteria and insects are some extreme cases of gene exchange between wide phylogenetic distances. An example is the presence of bacterial 'rol' genes from Agrobacterium species in tobacco (Nicotiniana) plants (Intrieri and Buiatti). Figure 1. Phylogenetic tree of life as proposed by Carl Woese In vertical gene transmission, genetic variability of a species mainly arises during meiosis by recombination of genes. According to Mendal’s law of inheritance, alleles of different genes assort independently during gamete formation and thereby produce novel gene combinations which in turn generate variability. Mutations, which are the random changes of gene sequence of a DNA strand, are considered as an error in the vertical gene transmission process. It can happen as a point mutation, chromosomal duplication, breaking and rearrangement of chromosomes and addition or deletion of chromosomes. When such mutant is passed down to the next generation, it is not a mutant anymore, but a variant or a novel type. The variants who survive according to Darwin’s theory of â€Å"survival of the fittest†, subsequently pass the novel characters to their offspring by sexual or asexual reproduction. HGT however, is not a mutation and is not involved in gamete formation or sexual reproduction. It moves transposable elements between distantly-related or unrelated genomes and thereby intervenes in the process of evolution by originating different cell types and cre ating variants in its own way. Two hypotheses are presented here as ‘Continual horizontal transfer hypothesis’ and ‘Early massive horizontal transfer hypothesis.’ (Jain, Rivera and Lake). According to the ‘Continual horizontal transfer hypothesis’, HGT is a continuous process during prokaryotic evolution whereas in the ‘Early massive horizontal transfer hypothesis’, a massive exchange of a few operational genes (genes involved in

Discuss the foreign policy positions of former President George Bush, Essay

Discuss the foreign policy positions of former President George Bush, Jr. and President Barack Obama in terms of realism and idealism - Essay Example Political realism highlights the role of the state and assumes that the state’s foreign policies are driven by the nation’s interest. It is primarily based on the state’s efforts to preserve its territory integrity as well as political autonomy. This means that the state interests are based on power and security. This power is defined in terms of military, economic, cultural, diplomatic and economic terms. In a realist state, every nation should use their resources in order to defend their nation. This concept is derived on the fact that the international environment is an anarchical environment. Therefore, regardless of the treaties made by the state, it is the duty of the state to defend its interest. According to the realism school of thought, the state is under no foreign authority (Crawford 15). Political idealism, also referred to as Wilsonian Idealism, holds that a state’s foreign policy should reflect the internal policy. Although it is based on human nature, it significantly puts ethics and morals into consideration. Idealist government fosters equal rights, democracy rule and religion in their foreign policy (Crawford 50). It is based on civilian-scientific development methods rather than war and power. The idealist state emphasizes on the international values rather than the nation’s interest. The doctrines of realism contradict those of the idealist school in that ethics and morality take a centre stage in idealism. During his campaign, the incumbent president George Bush openly declared that he was a realist who was committed to ending the Clinton doctrine and the indiscriminate use of the military force where they did not serve the interest of the US (Mackubin 24). During his campaign, he did not speak of democracy and freedom in the country. He clearly stated that, like his father, Bush was