genetic variation

Examples of genetic variation in the following topics:

• Genetic Variation

  • Genetic variation is a measure of the variation that exists in the genetic makeup of individuals within population.
  • Genetic variation is a measure of the genetic differences that exist within a population.
  • The genetic variation of an entire species is often called genetic diversity.
  • Populations of wild cheetahs have very low genetic variation.
  • This phenotypic variation is due at least partly to genetic variation within the coquina population.

• Gene Flow and Mutation

  • A population's genetic variation changes as individuals migrate into or out of a population and when mutations introduce new alleles.
  • Even a population that may initially appear to be stable, such as a pride of lions, can receive new genetic variation as developing males leave their mothers to form new prides with genetically-unrelated females.
  • This variable flow of individuals in and out of the group not only changes the gene structure of the population, but can also introduce new genetic variation to populations in different geological locations and habitats.
  • Maintained gene flow between two populations can also lead to a combination of the two gene pools, reducing the genetic variation between the two groups.
  • This mutation has introduce a new allele into the population that increases genetic variation and may be passed on to the next generation.

• Defining Population Evolution

  • Genetic variation in a population is determined by mutations, natural selection, genetic drift, genetic hitchhiking, and gene flow.
  • Five forces can cause genetic variation and evolution in a population: mutations, natural selection, genetic drift, genetic hitchhiking, and gene flow.
  • When recombination occurs during sexual reproduction, genes are usually shuffled so that each parent gives its offspring a random assortment of its genetic variation.
  • If advantageous, this gene variation may replace all the other variations until the entire population exhibits that trait.
  • Describe how the forces of genetic drift, genetic hitchhiking, gene flow, and mutation can lead to differences in population variation

• Processes and Patterns of Evolution

  • Natural selection can only occur in the presence of genetic variation; environmental conditions determine which traits are selected.
  • This is critical because variation among individuals can be caused by non-genetic reasons, such as an individual being taller due to better nutrition rather than different genes.
  • Mutation, a change in the DNA sequence, is the ultimate source of new alleles, or new genetic variation in any population.
  • Scientists describe groups of organisms becoming adapted to their environment when a change in the range of genetic variation occurs over time that increases or maintains the "fitness" of the population to its environment.
  • Explain why only heritable variation can be acted upon by natural selection

• Gene rearrangement within genomes

  • Genetic recombination is the process by which two DNA molecules exchange genetic information, resulting in the production of a new combination of alleles.
  • In eukaryotes, genetic recombination during meiosis can lead to a novel set of genetic information that can be passed on to progeny.
  • Crossing-over (homologous recombination) is one such mechanism by which DNA variations can occur, and genes can be rearranged.
  • This event results in variations of gametes that can produce variation in species.
  • Crossing over also accounts for genetic variation, because, due to the swapping of genetic material during crossing over, the chromatids held together by the centromere are no longer identical.

• Genetic Drift

  • Genetic drift is the converse of natural selection.
  • Small populations are more susceptible to the forces of genetic drift.
  • The bottleneck effect occurs when only a few individuals survive and reduces variation in the gene pool of a population.
  • The genetic structure of the survivors becomes the genetic structure of the entire population, which may be very different from the pre-disaster population.
  • Thus even while genetic drift is a random, directionless process, it acts to eliminate genetic variation over time.

• Advantages and Disadvantages of Sexual Reproduction

  • During sexual reproduction, the genetic material of two individuals is combined to produce genetically-diverse offspring that differ from their parents.
  • On the surface, creating offspring that are genetic clones of the parent appears to be a better system.
  • The only source of variation in asexual organisms is mutation.
  • Variation is the outcome of sexual reproduction, but why are ongoing variations necessary?
  • No single species progresses too far ahead because genetic variation among the progeny of sexual reproduction provides all species with a mechanism to improve rapidly.

• Variations in Size and Number of Genes

  • Genetic diversity refers to any variation in the nucleotides, genes, chromosomes, or whole genomes of organisms.
  • Nucleotide variation is measured for discrete sections of the chromosomes, called genes.
  • Within any single organism, there may be variation between the two (or more) alleles for each gene.
  • This variation is introduced either through mutation of one of the alleles, or as a result of sexual reproduction.
  • Describe how variations in the size and number of genes can arise through evolutionary mechanisms

• Genetic Maps

  • Genetic maps provide information about which chromosomes contain specific genes and precisely where the genes lie on that chromosome.
  • Early genetic maps were based on the use of known genes as markers.
  • Some genetic markers used in generating genetic maps are restriction fragment length polymorphisms (RFLP), variable number of tandem repeats (VNTRs), microsatellite polymorphisms, and the single nucleotide polymorphisms (SNPs).
  • SNPs are variations in a single nucleotide.
  • Describe the different types of genetic markers that are used in generating genetic maps of DNA

• No Perfect Organism

  • Natural selection cannot create novel, perfect species because it only selects on existing variations in a population.
  • Natural selection can only select on existing variation in the population; it cannot create anything from scratch.
  • Therefore, the process of evolution is limited by a population's existing genetic variance, the physical proximity of alleles, non-beneficial intermediate morphs in a polymorphic population, and non-adaptive evolutionary forces.
  • When a neutral allele is linked to beneficial allele, consequently meaning that it has a selective advantage, the allele frequency can increase in the population through genetic hitchhiking (also called genetic draft).
  • It is simply the sum of various forces and their influence on the genetic and phenotypic variance of a population.