Ensaio Opcional (10/03)
The discovery of structures and molecules involved in inheritance of features shed light into genetics and many other science fields. However, understanding how these molecules are connected in the process of inheritance is the great contribution of the central dogma of molecular biology. The idea of this dogma is mainly flow of information, i.e, how the information can be properly transfered from one source to another. Basically, DNA is the main source of information, which is copied into RNA and, finally to a particular protein. There are many other genetic, and even epigenetic, pathways to transfer information, though. Although this diversity of mechanisms is high, the universality of this dogma is beyond our understanding. First, the comparison of genetic material from many different species was made viable, because the genetic code of nucleotides are the same. The process of flow of information are also present both in local (e.g., cell division) and historical levels (e.g., evolution of phenotypes). Furthermore, even the flow of information from nucleotides to amino acids are global (despite a few particularities in some taxa). Therefore, there is no doubt that the formulation of the central dogma of molecular biology revolutionized the way we think about molecular process and evolution.
Acredito que a sentença- chave seria começar com: "the great contribution of the central dogma of molecular biology is the understanding…"
De resto achei que estava bem estruturado (sentenças claras objetivas, com seus devidos pontos finais)
Corrigido por Maila Beyer
Ensaio 2 (24/03)
Genetic drift and natural selection are the two main process involved in fixation of mutations in genetic material. Nonetheless, the impact of the first had been historically underestimated until the work of Kimura pointed it out. Many evolutionists and geneticists had treated natural selection as the leading process introducing variation in populations. This kind of thinking inevitably leads to the concept of adaptation, i. e., all variation is important for the fitness of the organism. However, Kimura made a very important contribution when analyzing available evidences of variation in nucleotides and proteins. Based on these observations and some estimates of general rates of substitution, he argues that natural selection alone could not produce such huge diversity. Genetic drift is, thus, brought back as a better explanation, suggesting that the majority of this mutations are neutral or nearly neutral. Some examples offered to clarify this issue are the degenerated code, especially the third position of the codon, and the substitution of amino acids in hemoglobins that do not alter its main function. Genetic drift, therefore, is not just some process, but it seems to be the principal cause of variation in populations, even more than natural selection. Additionally, the consequences derived from this explanation are also huge. Most of genetic (and even phenotypic!) variation is not an adaptation. They can just be irrelevant to the organism.
Comentário por Pietro Vicari
A linguagem do texto está clara e bastante objetiva. As sequências me parecem claramente conectadas o que o torna o texto fluido.
Senti falta de citações que suportassem as afirmações contidas no texto. Na esfera conceitual um destaque para a frase "Many evolutionists and geneticists had treated natural selection as the leading process introducing variation in populations".
A seleção não introduz as variações nas populações, apenas seleciona a variabilidade que surge por outros processos. No mais considero seu ensaio bom e acredito que aprendi fazendo a revisão.
Ensaio 3 (31/03)
The role and intensity of both genetic drift and selection in molecular evolution have been intensively debated in the last decades. However, is it possible to verify which is more frequent in a given system? The effective population size (Ne) is an important concept used to understand the effects of these two process. Basically, Ne can be defined as the individuals of a given population that contribute to the genetic composition of the next generation. There are many factors that influence Ne, such as sex ratio, inbreeding, frequency and inheritance of alleles, changes in population size, and geographic or genetic subpopulations. There are many models that incorporate these factors to calculate Ne. Nevertheless, the generic effect of Ne in genetic drift and selection can be easily understood. Populations with low Ne are submitted more intensively to genetic drift. Although genetic drift still acts in populations with higher Ne values, selection tends to be more effective in fixation of alleles.