But how does genetic variation increase or decrease? And what effect do fluctuations in genetic variation have on populations over time? Mating patterns are important. Random forces lead to genetic drift. If the individuals at either end of the range reconnect and continue mating, the resulting genetic intermixing can contribute to more genetic variation overall. However, if the range becomes wide enough that interbreeding between opposite ends becomes less and less likely, and the different forces acting at either end become more and more pronounced, and the individuals at each end of the population range may eventually become genetically distinct from one another.
Here is an example of migration affecting relative allele frequency:. The overall effect. Here is an example of how a specific genotype is less favorable than another genotype:. Genetic variation in a population is derived from a wide assortment of genes and alleles. The persistence of populations over time through changing environments depends on their capacity to adapt to shifting external conditions.
Sometimes the addition of a new allele to a population makes it more able to survive; sometimes the addition of a new allele to a population makes it less able. Still other times, the addition of a new allele to a population has no effect at all, yet the new allele will persist over generations because its contribution to survival is neutral.
Key Questions How can genetic variation influence evolution? What is an example of genetic drift? Topic rooms within Genetics Close. No topic rooms are there. Browse Visually. Other Topic Rooms Genetics. Student Voices. Creature Cast. Cite Cite Robert C. Select Format Select format.
Permissions Icon Permissions. Abstract Small populations lose genetic variability because of genetic drift, and inbreeding within populations can further decrease individual variability.
Issue Section:. Download all slides. View Metrics. Email alerts Article activity alert. Advance article alerts. New issue alert. Because natural selection acts directly only on phenotypes, more genetic variation within a population usually enables more phenotypic variation. Other new alleles may be immediately detrimental such as a malformed oxygen-carrying protein and organisms carrying these new mutations will die out. Neutral alleles are neither selected for nor against and usually remain in the population.
Genetic variation is advantageous because it enables some individuals and, therefore, a population, to survive despite a changing environment. Some species display geographic variation as well as variation within a population. Geographic variation, or the distinctions in the genetic makeup of different populations, often occurs when populations are geographically separated by environmental barriers or when they are under selection pressures from a different environment. One example of geographic variation are clines: graded changes in a character down a geographic axis.
The genes that are encoded within these proteins are what enable cells to function. Most organisms that reproduce sexually have two copies of each gene , because each parent cell or organism donates a single copy of its genes to its offspring. Additionally, genes can exist in slightly different forms, called alleles, which further adds to genetic variation. The combination of alleles of a gene that an individual receives from both parents determines what biologists call the genotype for a particular trait, such as hair texture.
The genotype that an individual possesses for a trait, in turn, determines the phenotype —the observable characteristics—such as whether that individual actually ends up with straight, wavy, or curly hair. Genetic variation within a species can result from a few different sources. Mutations, the changes in the sequences of genes in DNA , are one source of genetic variation.
Another source is gene flow , or the movement of genes between different groups of organisms. Finally, genetic variation can be a result of sexual reproduction , which leads to the creation of new combinations of genes. Genetic variation in a group of organisms enables some organisms to survive better than others in the environment in which they live.
Organisms of even a small population can differ strikingly in terms of how well suited they are for life in a certain environment. An example would be moths of the same species with different color wings. Moths with wings similar to the color of tree bark are better able to camouflage themselves than moths of a different color.
As a result, the tree-colored moths are more likely to survive, reproduce, and pass on their genes.
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