However, existing genes can be arranged in new ways from chromosomal crossing over and recombination in sexual reproduction. Overall, the main sources of genetic variation are the formation of new alleles, the altering of gene number or position, rapid reproduction, and sexual reproduction.
Learning Objectives Assess the ways in which genetic variance affects the evolution of populations. 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 Variation Genetic variation is a measure of the genetic differences that exist within a population. Genetic variation is caused by: mutation random mating between organisms random fertilization crossing over or recombination between chromatids of homologous chromosomes during meiosis The last three of these factors reshuffle alleles within a population, giving offspring combinations which differ from their parents and from others.
This phenotypic variation is due at least partly to genetic variation within the coquina population. Evolution and Adaptation to the Environment Variation allows some individuals within a population to adapt to the changing environment. In other words, some genotypes will be favored, and individuals with those genotypes will continue to reproduce. Other genotypes will not be favored: individuals with those genotypes will be less likely to reproduce.
What type of genotype would be unfavorable? Unfavorable genotypes take many forms, such as increased risk of predation, decreased access to mates, or decreased access to resources that maintain health.
Overall, the forces that cause relative allele frequencies to change at the population level can also influence the selection forces that shape them over successive generations. For example, if moths with genotype aa migrate into a population composed of AA and Aa individuals, they will increase the relative allele frequency of a. However, if the aa genotype has a clear disadvantage to survival e.
This page appears in the following eBook. Aa Aa Aa. Genetic variation describes naturally occurring genetic differences among individuals of the same species. This variation permits flexibility and survival of a population in the face of changing environmental circumstances. Consequently, genetic variation is often considered an advantage, as it is a form of preparation for the unexpected.
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. This is known as natural selection. Related Content:. What is DNA? What is a gene? What is inheritance? What is evolution? What is a genetic disorder? What is a mutation? What is pharmacogenomics?
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