Mechanisms behind cellular differentiation are the same as why organisms change in nature - Epigenetics
Excerpts: "All our cells contain more or less identical deoxyribonucleic acid (DNA). Yet they constitute organs each with specific tasks and roles in our body. The genome in every cell is the same, but the epigenome is different and this contributes to differences in protein expression."
"The epigenome refers to all epigenetic marks on the genome, in other words the overall epigenetic state or functional genome of the cell. Epigenetics, which literally means on top of genetics, is defined as the mechanisms of heritable, over cell divisions, specific cell functions or phenotypes that do not directly involve the primary DNA sequence. Epigenetic mechanisms enable the environment to interact with genes, switching them on and off, and this regulates the plasticity of the cell phenotype. This functional genome with DNA transcription and ribonucleic acid (RNA) translation is responsible for the protein expression in each cell and, ultimately, the phenotype."
During butterfly metamorphosis the DNA is the same in all four stages but epigenome is different.
"Epigenetics is a dynamic process in cell differentiation that was first described by Waddington in the 1950s. He depicted an epigenetic landscape and described epigenetics as the branch of biology that studies the causal interactions between genes and their products, which brings the phenotype into being. Epigenetic marks change, and make changes, as cells differentiate and this process can persist through mitosis and meiosis as cells divide."
"The modern definition of epigenetics refers to a modification that is not a mutation and that is initiated by a signal. It is inherited during mitosis, even in the absence of this signal, and that affects the regulation of gene transcription and ultimately protein translation. Mechanisms can be pre‐ or post‐translational, such as DNA methylation and histone modification, respectively. Epigenetic modifications change the accessibility of DNA for transcription to RNA in different ways. The most studied epigenetic mechanism is DNA methylation, as methylation is stable, DNA is easy to extract from cells and possible to store."
A few examples of epigenetic regulation and how it affects the phenotype:
A soldier or a worker ant? This is regulated by epigenetic mechanisms and factors. No mutations, no selection.
Diet of royal jelly during larval development generates queen bees. The DNA is the same as in workers.
Darwin's finches are different due to changes in diet types. Nothing to do with random mutations and evolution. This is ecological adaptation and epigenetic regulation.
The new study shows that epigenetic-based silencing of a large set of genes limits the eye development of cave-dwelling A. mexicanus fish.
My comment: Ecological adaptation, organismal change, phenotypic change and variation are always based on epigenetic regulation of pre-existing biological information. Epigenetic modifications, however, often result in minor errors in underlying DNA. This makes genomes weaker mostly due to tendency of GC-content turning to AT-content. Consequences are observable; weakening immune systems, smaller organisms, extinction etc. Nothing is evolving on this planet. Don't get lost, my friends.
