Question

4. List and describe the mechanisms of evolution. Within a population of a species, which are most important for the creation of variation and which are most important for limiting that variation?

Answer 1

Evolution leads to the introduction, alteration and deletion of inheritable features or traits in order to come up with combination of traits that would make an organism fit for the changing environment. The evolutionary forces are acting real time to change certain inheritable traits bit by bit by accumulating variations that is fit for the changing environmental condition. The mechanisms of evolution or the forces that drive evolution are as follows:

1. Mutation: Mutaions are the alterations in DNA sequences of individuals in a population that leads to an altered phenotypic expressions. These changes are inheritable from one generation to another. The mutations can arise due to faulty DNA repair mechanisms, crossing over during meotic phases of cell division or due to environmental factors. Accumulation of mutation leads to greater degree of variations. These variations then accumulate further to pave the path for evolution.
2. Natural Selection: It is a phenomenon of where the population with certain traits get selected over another population of same species but a different version of the trait by the surrounding environmental condition. Natural conditions select the best candidate and the rest would not get a chance for survival. For example, white colored mice living on dark colored rocks are an easy target for predatory birds while the black mice population survives and flourishes on the black rocks as they are hard to detect. This is a natural selection of the black mice on the black rocks.
3. Genetic drift: A sudden change in allele frequencies of a particular gene in a population due to the chance occurrence of an event that eliminated one of the allele variant. For example, let us consider a beetle population of red and blue. The lived on the bushes of a particular region in the forest. All of a suddent an elephant stamped up on them and as a chance most blue beetles came under the elephant foot. The would cause the red beetle population to predominate that bush and grow in number over time.
4. Migration: Migration of individuals from a certain population containing a specific trait to another population and introducing this novel trait (for the new population)  also drives evolution. This is the gene flow of the variant allele from one population to another altering the prevailing allele frequencies in the second population.

Within a population of a species, the important factors for the creation of variation are mutations and gene flow. Mutations alter the genetic code contributing directly to the occurrence of variation. Gene flow introduces new variants of a gene by crossing population boundaries.

The important evolutionary forces that are limiting to the accumulation of variations are natural selection and genetic drift. Natural selection is limiting to variations beacuse not all variations (alterations in genetic sequences) will get selected. The environment will be the ultimate decision maker for whether a variation will survive the natural slection pressure. Unfavourable favourable variations will not survive beyond a few generations. Genetic drift is also another limitation. For instance, a variation arose due to a certain interesting mutation on a specific gene. But due to a genetic drift that variation got lost (imaging elephant stamping upon these individuals carring the variation). This variation will never get a chance to be passed on to future generations.