What Is Genetic Variation? Sources, Definition,and Types
Heritable genetic variation is essential for some basic mechanisms of evolutionary change. Contrary to what was believed during the Darwin era (namely that heritable material blends together from two parents to produce characteristics that can be seen in the offspring), Gregor Mendel, the father of modern genetics, demonstrated in his studies that inheritance is particulate. This means that the heredity factors—or genes—remain unchanged in the offspring.
However, genetic variation alone cannot be the only driving factor for evolution. What this means is that there has to be a steady and continuous origin of new genetic variation, or a natural selection, so to speak.
But before diving deeper into the reasons behind genetic variation, let us back up a few steps and define a few things so that this story becomes a bit easier to follow. Simply put, genetic variation refers to differences in genetic material that largely refers to your DNA sequence that is located on chromosomes. These DNA sequences also make up all kinds of different genes. And by virtue of DNA being on chromosomes, genes are on chromosomes as well. Genes are characterized based on the sequences of their basic building blocks, namely nucleotides. These genes always code for the same specific proteins, unless a gene’s sequence has changed for some reason and caused it to code for a completely different protein or perhaps not even code for a protein at all. It is these very changes in the DNA sequences that lead to genetic variation, and there are several reasons due to which changes in DNA sequences take place.
Sources of Genetic Variation
Where does genetic variation come from? What triggers this process that is so essential for all life to evolve appropriately? There are three main sources of genetic variation, each of which will be discussed in a bit more detail.
Mutations refer to small changes in the DNA sequence. One single mutation can have drastic effects on the downstream events. However, large evolutionary changes are vastly due to the accumulation of several mutations. Overall, there are two different kinds of mutations, namely point mutations and chromosomal mutations. While point mutations affect only one or a few nucleotides, chromosomal mutations have a much bigger effect by affecting the actual number of chromosomes of a system or the number of arrangements of genes in a chromosome. The latter inadvertently also affects the chromosomal shape.
As the actual name implies, a point mutation refers to a change in one to a few nucleotides in one gene. Point mutations can be further categorized into base pair substitutions and base pair insertions or deletions. Within the category of point mutations are base pair substitutions that are marked by a replacement of nucleotides with another pair of nucleotides. Insertions and deletions are either additions or losses of one or more nucleotide pairs in a gene.
As mentioned above,these types of mutations are marked by a change in the number of chromosomes or the order of genes in one chromosome. Some examples of chromosomal mutations include deletions that refer to a complete loss of a chromosome segment; duplications that refer to a chromosome segment exists more than once in a set of chromosomes; and inversions that refer to a chromosome breaking twice and a rotation of 180oC of the broken segment. Translocations refer to an event during the chromosomal segment location is changed. Furthermore, there are also instances during which the number of chromosomes changes. This typically has a lot more serious consequences. These events include centric fusion during which two chromosomes fuse into one; centric fission, whereby one chromosome splits into two parts; aneuploidy, referring to either excess or shortage of chromosomal material; and polyploidy that refers to chromosomal duplications that result in individuals having more than the usual number of 46 chromosomes. Several genetic diseases are the result of aneuploidy.
2. Gene Flow
Gene flow or the flow of genes refers to the actual movement of genes between populations. Some populations have more of one specific gene while others have more of another specific gene. Sometimes, these genes cross between different cultures, and this is a significant source of genetic variation.
Sex can actually lead to the introduction of new genetic combinations into a single population. This shuffling of genes is yet another significant sources of variability among genes or genetic variation.
Hopefully, after the elaboration so far, it is evident that without genetic variation, evolution (including human populations) cannot take place. Genetic variation predominantly takes place due to mutations. Alleles are generated due to point mutations. In other words, if an existing allele undergoes a point mutation, that allele produces yet another allele. Most of the point mutations are deleterious. If they are not, they are recessive and thus masked. Unlike point mutations, chromosomal mutations mainly shuffle around existing alleles, either within a chromosome whereby the mutations are moved from one area of the chromosome to another or from one chromosome to an entirely different one.
Chromosomal mutations primarily move existing alleles around—either from one location on a chromosome to another on the same chromosome or from one chromosome to a different chromosome. Ultimately, the events of crossing over, independent assortment, and sex are the main mechanism that upholds genetic diversity within populations that maintain genetic diversity within populations.
So, now that you are a bit more aware of genetic variation and how it is actually a very important aspect of survival, it is much easier to appreciate the different ways in which we are all unique. The term “mutation” has largely had a negative connotation.Hopefully, after reading all this, your opinion has shifted a bit more toward the positive when it comes to the word.