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Any interactives on this page can only be played while you are visiting our website. You cannot download interactives. In the mids, Charles Darwin famously described variation in the anatomy of finches from the Galapagos Islands.
Alfred Russel Wallace noted the similarities and differences between nearby species and those separated by natural boundaries in the Amazon and Indonesia. Independently they came to the same conclusion: over generations, natural selection of inherited traits could give rise to new species.
Use the resources below to teach the theory of evolution in your classroom. Genes are units of hereditary information. A gene is a section of a long molecule called deoxyribonucleic acid DNA. Genetics is the study of genes and how traits are inherited—or passed down—from one generation to the next.
Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Skip to content. Image genetic variation In many species, special genetic variations give animals a camouflaged appearance to blend in with their environment, like this Catalpa Sphinx moth Ceratomia catalpae which uses its textured wings to blend in with a tree's bark.
Photograph by J. Twitter Facebook Pinterest Google Classroom. Encyclopedic Entry Vocabulary. Media Credits The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. Regina Bailey is a board-certified registered nurse, science writer and educator. Updated August 21, Key Takeaways: Genetic Variation Genetic variation refers to differences in the genetic makeup of individuals in a population.
Genetic variation is necessary in natural selection. In natural selection, organisms with environmentally selected traits are better able to adapt to the environment and pass on their genes.
Major causes of variation include mutations, gene flow, and sexual reproduction. DNA mutation causes genetic variation by altering the genes of individuals in a population.
Gene flow leads to genetic variation as new individuals with different gene combinations migrate into a population. Sexual reproduction promotes variable gene combinations in a population leading to genetic variation. Examples of genetic variation include eye color, blood type, camouflage in animals, and leaf modification in plants.
Featured Video. Cite this Article Format. Bailey, Regina. Genetic Variation Definition, Causes, and Examples. A Genetics Definition of Homologous Chromosomes. Synonymous vs. Nonsynonymous Mutations. Genetically Modified Organisms and Evolution. Your Privacy Rights. Explain how environmental variance and nonrandom mating can change gene frequencies in a population. If individuals nonrandomly mate with other individuals in the population, i.
There are many reasons nonrandom mating occurs. One reason is simple mate choice or sexual selection; for example, female peahens may prefer peacocks with bigger, brighter tails. Traits that lead to more matings for an individual lead to more offspring and through natural selection, eventually lead to a higher frequency of that trait in the population.
Assortative mating in the American Robin : The American Robin may practice assortative mating on plumage color, a melanin based trait, and mate with other robins who have the most similar shade of color. However, there may also be some sexual selection for more vibrant plumage which indicates health and reproductive performance. Another cause of nonrandom mating is physical location.
This is especially true in large populations spread over large geographic distances where not all individuals will have equal access to one another. Some might be miles apart through woods or over rough terrain, while others might live immediately nearby. Genes are not the only players involved in determining population variation.
Phenotypes are also influenced by other factors, such as the environment. A beachgoer is likely to have darker skin than a city dweller, for example, due to regular exposure to the sun, an environmental factor. Some major characteristics, such as gender, are determined by the environment for some species. For example, some turtles and other reptiles have temperature-dependent sex determination TSD. TSD means that individuals develop into males if their eggs are incubated within a certain temperature range, or females at a different temperature range.
Temperature-dependent sex determination : The sex of the American alligator Alligator mississippiensis is determined by the temperature at which the eggs are incubated. Eggs incubated at 30 degrees C produce females, and eggs incubated at 33 degrees C produce males. Geographic separation between populations can lead to differences in the phenotypic variation between those populations. Such geographical variation is seen between most populations and can be significant.
One type of geographic variation, called a cline, can be seen as populations of a given species vary gradually across an ecological gradient. Geographic variation in moose : This graph shows geographical variation in moose; body mass increase positively with latitude. This is considered a latitudinal cline. Alternatively, flowering plants tend to bloom at different times depending on where they are along the slope of a mountain, known as an altitudinal cline.
If there is gene flow between the populations, the individuals will likely show gradual differences in phenotype along the cline. Restricted gene flow, on the other hand, can lead to abrupt differences, even speciation.
Privacy Policy. Skip to main content. The Evolution of Populations. Search for:. Population Genetics. Genetic Variation Genetic variation is a measure of the variation that exists in the genetic makeup of individuals within population. Learning Objectives Assess the ways in which genetic variance affects the evolution of populations.
Key Takeaways Key Points Genetic variation is an important force in evolution as it allows natural selection to increase or decrease frequency of alleles already in the population.
Genetic variation is advantageous to a population because it enables some individuals to adapt to the environment while maintaining the survival of the population. Key Terms genetic diversity : the level of biodiversity, refers to the total number of genetic characteristics in the genetic makeup of a species crossing over : the exchange of genetic material between homologous chromosomes that results in recombinant chromosomes phenotypic variation : variation due to underlying heritable genetic variation ; a fundamental prerequisite for evolution by natural selection genetic variation : variation in alleles of genes that occurs both within and among populations.
Genetic Drift Genetic drift is the change in allele frequencies of a population due to random chance events, such as natural disasters. Learning Objectives Distinguish between selection and genetic drift.
Key Takeaways Key Points Genetic drift is the change in the frequency of an allele in a population due to random sampling and the random events that influence the survival and reproduction of those individuals. The bottleneck effect occurs when a natural disaster or similar event randomly kills a large portion i. The founder effect occurs when a portion of the population i. Small populations are more susceptible genetic drift than large populations, whose larger numbers can buffer the population against chance events.
Key Terms genetic drift : an overall shift of allele distribution in an isolated population, due to random sampling founder effect : a decrease in genetic variation that occurs when an entire population descends from a small number of founders random sampling : a subset of individuals a sample chosen from a larger set a population by chance.
Learning Objectives Explain how gene flow and mutations can influence the allele frequencies of a population. Key Takeaways Key Points Plant populations experience gene flow by spreading their pollen long distances.
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