Gene duplication Gene duplication is the process by which a region of DNA coding for a gene is duplicated.
A substantial part of the phenotypic variation in a population is caused by genotypic variation. The frequency of one particular allele will become more or less prevalent relative to other forms of that gene.
Variation disappears when a new allele reaches the point of fixation —when it either disappears from the population or replaces the ancestral allele entirely. Before the discovery of Mendelian genetics, one common hypothesis was blending inheritance. But with blending inheritance, genetic variance would be rapidly lost, making evolution by natural selection implausible.
The Hardy—Weinberg principle provides the solution to how variation is maintained in a population with Mendelian inheritance. The frequencies of alleles variations in a gene will remain constant in the absence of selection, mutation, migration and genetic drift.
Despite the constant introduction of new variation through mutation and gene flow, most of the genome of a species is identical in all individuals of that species. When mutations occur, they may alter the product of a geneor prevent the gene from functioning, or have no effect.
This process is easier once a gene has been duplicated because it increases the redundancy of the system; one gene in the pair can acquire a new function while the other copy continues to perform its original function. Sexual reproductionGenetic recombinationand Evolution of sexual reproduction In asexual organisms, genes are inherited together, or linked, as they cannot mix with genes of other organisms during reproduction.
In a related process called homologous recombinationsexual organisms exchange DNA between two matching chromosomes. If each individual were to contribute to the same number of offspring twoa the sexual population remains the same size each generation, where the b Asexual reproduction population doubles in size each generation.
The two-fold cost of sex was first described by John Maynard Smith. This cost does not apply to hermaphroditic species, like most plants and many invertebrates.
The Red Queen hypothesis has been used to explain the significance of sexual reproduction as a means to enable continual evolution and adaptation in response to coevolution with other species in an ever-changing environment. Gene flow Gene flow is the exchange of genes between populations and between species.
Gene flow can be caused by the movement of individuals between separate populations of organisms, as might be caused by the movement of mice between inland and coastal populations, or the movement of pollen between heavy metal tolerant and heavy metal sensitive populations of grasses.
Gene transfer between species includes the formation of hybrid organisms and horizontal gene transfer. Horizontal gene transfer is the transfer of genetic material from one organism to another organism that is not its offspring; this is most common among bacteria.
It is possible that eukaryotes themselves originated from horizontal gene transfers between bacteria and archaea. From a Neo-Darwinian perspective, evolution occurs when there are changes in the frequencies of alleles within a population of interbreeding organisms.
Mechanisms that can lead to changes in allele frequencies include natural selection, genetic drift, genetic hitchhiking, mutation and gene flow. Natural selection Further information: Sexual selection Evolution by means of natural selection is the process by which traits that enhance survival and reproduction become more common in successive generations of a population.
It has often been called a "self-evident" mechanism because it necessarily follows from three simple facts: Different traits confer different rates of survival and reproduction differential fitness.
These traits can be passed from generation to generation heritability of fitness. More offspring are produced than can possibly survive, and these conditions produce competition between organisms for survival and reproduction.
Consequently, organisms with traits that give them an advantage over their competitors are more likely to pass on their traits to the next generation than those with traits that do not confer an advantage.
The central concept of natural selection is the evolutionary fitness of an organism. These traits are said to be "selected for. Conversely, the lower fitness caused by having a less beneficial or deleterious allele results in this allele becoming rarer—they are "selected against.
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