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Genetic variance is the result of several factors, leading to the evolution of a species. It is influenced by several main criteria, including genetic mutation, the genetic elimination of recessive characteristics and addition of dominant ones, and the size of the available gene pool. Genetic variance can cause differences at an observable or phenotypic level in species, leading to explanations for things such as blood type, skin color and size.
In humans and similar organisms, the genetic code carries a pair of each type of gene. The two components, called alleles, may be identical or different from one another, and are often characterized as dominant or recessive. For instance, if a person has brown eyes, they have at least one brown-eye causing allele, because brown eye color is a dominant trait. Because blue eyes are a recessive trait, a blue-eyed person has identical blue-eye causing alleles.
While that seems somewhat straightforward, the science of genetic variance quickly becomes more complex. Some alleles are neither dominant nor recessive, and may combine to create a new hybrid in the next generation. In some flowers, crossbreeding a red flower and a white flower may result in a red or white flower, or it may result in a pink or striped hybrid. In cats, several different colored kittens may be born in the same litter, directly affected by genetic variance.
Variance can also be caused by gene mutation. If a parent's genes become altered by an exterior force, such as radiation or a virus, it can add a new element into the gene pool of the next generation. Mutations can be beneficial to the survival of the species, such as a color variance that causes a species to be harder for predators to see. In this case, the survival rate of creatures with the mutation may increase, causing them to eventually be the dominant faction of the population. Natural selection can also eliminate negative traits, by lowering the survival rate or shortening the life span of a mutated gene carrier.
The size of the gene pool can seriously affect genetic variance, preventing undesirable traits from being washed out of a community as those with similar genetic codes reproduce. A population forced to reproduce with close relatives can reduce the amount of genetic variance, often making recessive or undesirable characteristics grow over time, as carriers of a particular gene continue to breed. More than any social or cultural construct, it is for evolutionary purposes that it remains unwise to mate with close relatives.
Genetic variance is what allows for species adaptation over time. Whether through gene combinations in offspring or mutation, strong survival traits will tend to grow more dominant in a population. Alterations at the phenotype levels of physical traits, inherited behavior, or other observable characteristics can have an enormous affect on how a species survives in its environment. Generally, the wider the gene pool, the more successful the population, as genetic variance will weed out the poor survival traits and give dominance to the most successful.