Genetic variation has many important parts to it, a big portion being mutation. A mutation is a change in the nucleotide sequence of DNA dealing with its genes and alleles. A point mutation is a change in a single base in a nucleotide sequence. That being said, the origin of how a mutation forms is mutagenesis. There are three types of point mutations: substitution, frame shift(insertion and deletion), and an editing error. Substitution is the replacement of one nucleotide and its partner with another pair of nucleotides. A frame shift mutation occurs whenever the number of nucleotides inserted or deleted is not a multiple of three. While dealing with mutations, several characteristics must also be included. These are randomness, non-directionality, change in phenotypic traits, and gametic change. These all contribute to how a mutation may be classified going from physical descriptions to the very gametes themselves. An example of a mutation could occur when sickle cell anemia occurs because of a mutation in protein structure.
The following part deals with chromosomal mechanisms. There are four different results that occur when there is chromosomal breakage. A deletion occurs when a chromosomal fragment lacking a centromere is lost. Sometimes a deleted fragment may become attached as an extra segment to a sister chromatid, producing a duplication. A chromosomal fragment may also reattch to the original chromosome but in the reverse orientation, producing an inversion. A fourth possible result of chromosomal breakage is for the fragment to join a nonhomologous chromosome, a rearrangement called a translocation. Crossing over greatly contributes to genetic variation in the fact that it is the reciprocal exchange of genetic material. When there is an abnormal chromosome number, an aneuploidy can occur. The chromosomal alteration for organisms that havemore than two complete chromosome sets is polyploidy. Some other mechanisms are transposable elements, virus induced charges, and genetic engineering. A transposable element is a segment of genetic material that is able to change its position in the genome. Genetic engineering is a technique used to duplicate or manipulate genetic material. The changes induce by a virus is also classified in this category of chromosomal mechanisms.
The way in offspring are even produced is by sexual reproduction. When two parents contribute genetic material, they go through meiosis and crossing over occurs, which reshuffles traits promoting diversity. Recombination occurs when individual chromosomes that carry genes derived from two different parents. The principle in which each homologous pair of chromosomes is positioned independently of the other pairs into daughter cells is called independent assortment. Random fertilization adds to the genetic variation arising from meiosis. When offspring are created with gene pool connection, it is called cross breeding.
Darwin’s theory of natural selection is divided into five observations. For any species, population sizes would increase exponentially if all individuals that are born reproduced successfully and so there is differential success. Nonetheless, populations tend to remain stable in size, except for seasonal fluctuations. Resources are limited and production of more individuals than the environment can support leads to struggle for existence. Much of this variation is heritable. When environmental conditions or food sources change, adaptations may occur so that the organism can better live and reproduce. Adaptive radiation is the evolution of many diversely adapted species from a common ancestor upon introduction to various new environmental opportunities and challenges. Variation is important because without it, a species will be same all around with the same flaws and it will have less of a chance of survival. In order for there to be variation, there must be a population and not just a few individuals. An example of natural selection would be in guppy populations with differential predation based on size among other things.
The process by which genes from one population transfer to another of the same species is called gene flow, in which alleles either leave or come in. The ways in which gene flow is accomplished are through outbreeding and geographic isolation. Outbreeding is when selected individuals breed outside the limits of the variety. The standard dealing with geographic isolation is when there are physical barriers preventing any gene flow at all. Some more barriers include addition, removal, temporal, reproductive, and behavioral. An example of this may be in reproductive barriers in which two species cannot mate because of differences on a reproductive base.
In small populations, random changes in the frequency of alleles refer to genetic drift. When a few individuals become isolated from a larger population, this smaller group may establish a new population whose gene pool is not reflective of the source population and this is called the founder effect. Another effect if called the bottleneck effect in which a population is reduced such that the surviving population is no longer genetically representative of the original population. It can be concluded that a small population has a much smaller chance of survival than that of a large population. An example of this would be when a species of elephant seals is greatly reduced. When they are rebounded, there is no variation to be found.
The last part contributing to gene variation is assortative mating. This is the reproductive pairing of individuals that have more traits in common than would likely be the case if mating were random. Three forms of this are sexual selection, artificial selection, and in-breeding. Sexual selection is when a certain sex of a species selects mates based on certain characteristics. Artificial selection occurs when an outside source chooses certain traits desired to them using inheritable characteristics. The form in which individuals are bred with close relatives is called inbreeding and it leads to reduction in genetic diversity. An example of this could be when watermelons are grown with no seeds to better suit those who eat it, a form of artificial selection.