Genetic variation refers to the differences in DNA sequences among individuals in a population. These genetic distinctions are the reason that, with the exception of identical twins, no two members of a species are exactly the same. This diversity provides the foundation for the vast array of organisms seen on Earth.
Observable Examples of Genetic Variation
The results of genetic variation are visible in the physical differences between individuals. In humans, this is apparent in the wide spectrum of hair colors, skin tones, and eye colors. Different versions of genes, called alleles, lead to the variety we see. For example, the amount of melanin pigment, dictated by genetic instructions, determines whether a person’s eyes are brown or blue.
This principle extends throughout the animal kingdom. Domestic dog breeds, from the short-legged Corgi to the towering Great Dane, showcase physical differences stemming from variations within a single species’ gene pool. The diverse shell patterns and colors found on a single species of snail are also outward expressions of underlying genetic differences.
Plants also exhibit clear examples of genetic variation. Different cultivated varieties of apples, such as the green, tart Granny Smith and the sweet Red Delicious, are the product of genetic divergence. The array of colors seen in flowers like tulips also demonstrates this principle. In some cases, variations can be specialized, such as the modified leaves of carnivorous plants developed to suit a specific way of life.
Underlying Causes of Variation
The differences observed in populations arise from a few core processes. The primary source of all new genetic information is mutation, which is a change in the DNA sequence. These random changes can be compared to a “typo” in the genetic code. While many mutations have no effect or can be detrimental, some can introduce new, beneficial traits into a population.
Another source of genetic variation comes from the shuffling of existing genes during sexual reproduction. When two parents reproduce, their genes are combined in novel ways in their offspring. This process, known as genetic recombination, is similar to shuffling a deck of cards to create a new hand.
The Role of Variation in Survival
Genetic variation is a population’s toolkit for survival in a changing world. A diverse gene pool increases the likelihood that some individuals will have traits that allow them to withstand new environmental pressures or diseases. This variation is the raw material upon which natural selection acts.
An illustration of this is the peppered moth in England. The population included both light-colored and dark-colored individuals. Before the Industrial Revolution, light-colored moths were well-camouflaged against lichen-covered trees. As industrial pollution darkened the tree bark, the dark-colored moths became better camouflaged and less likely to be eaten by birds.
This shift gave the dark moths a survival advantage, and they became more common. The initial variation within the moth population allowed the species to adapt to the changing conditions.