Essay 1 March 17th
What does replication implies to phylogenetics?
The dichotomous nature of DNA's replication is the cornerstone of phylogenetics. One lineage spliting in two is a reflex of one molecule of DNA duplicating itself. This process is a very delicate one and, to prevent undesired and/or harmful effects, a complex machinery acts repairing whenever a mistake happens. Damage to the DNA can be done in various forms, be it chemichal, mechanical or through radiation. Although very efficient, this system is not perfect and sometimes errors can slip through, whenever this happens we call it a mutation. If this mutation can be passed down and spread to the population (thus not being restrained to the individual or molecule where it appeared), it's called a substitution. When a change, or the accumulation of changes, are enough to reproductive isolate one lineage from another, speciation occurs. An issue with our current paradigm is that it is built only based in vertical transfers of information. In nature, mainly in prokaryotes, it's common to have horizontal transfers of genetic material. Albeit knowing how this phenom happens, we are not able to fully understand it under phylogenetic lenses.
Essay 2 March 24th
The Neutral Theory of Molecular Evolution
It’s a common thought that a mutation must be either positive or negative for an organism. In 1968, Mooto Kimura, a Japanese geneticist showed that vast part of mutations in genome are neutral. That implies they are not being fixed through natural selection. Kimura’s Neutral Theory states that random fixation of neutral or very nearly neutral mutations through drift in finite populations is cause behind the majority of evolutionary changes. By neutral we understand that those variants doesn’t interfere in the organism’s fitness. This proposal clashed with the Neo-Darwinians at time, for their thought that natural selection is the main driving force behind evolutionary changes. Data found comparing hemoglobin and other molecules of “living fossils” (organisms that have gone trough few evolutionary chances since they appeared on Earth) with rapid evolving species show that they have undergone the same number of nucleotids substitutions. This evidence gives support to Kimura’s predictions.
Comentários por Priscilla Afonso:
Excelente o texto! Você usou frases curtas e conseguiu explicar muito bem o assunto da aula passada. A única coisa que difere das sugestões feitas pelo professor é sobre o uso de referências que devem vir no final de cada frase. Mas você realmente transmitiu muito bem a informação.