Advanced searches left 3/3
Search only database of 8 mil and more summaries

The Evolution Of Populations Due To Chance

Summarized by PlexPage
Last Updated: 02 July 2021

* If you want to update the article please login/register

General | Latest Info

Natural selection. C. Has more effect in large populations than in small populations. D. Genetic drift. E. Gene flow. The correct answer is D. Genetic drift. The theory of evolution states that organisms have changed over time. It is the genetic makeup of these organisms that has evolved, resulting in different species that are alive today. It has long been recognized that genetic variation is needed in order for species to evolve. Diagram showing genetic drift. Shift occur in red versus blue genes of the population over time. Gringer research studies and intermediate fossils provide a lot of evidence in support of the theory of evolution. Natural selection was thought by Charles Darwin to be the main mechanism responsible for the evolution of life on earth. Selection is based on the idea that some individuals that are better able to survive will be more likely to leave more offspring than other individuals in the population. Over time, then genotypes of fitter individuals will become more frequent in the population, and it thus evolve. Other researchers believe that gene mutation, genetic drift, and gene flow are also very important mechanisms of evolution. A mutation is an alteration in the genotype which can be helpful, harmful or have no effect on survival. Genetic drift is a random change in frequency of genotypes. This can occur after random event such as a natural disaster eliminates some genotypes in the population. Genetic drift has the biggest impact on small populations that have limited gene flow. Gene flow is the migration of individuals into and out of the population. It is this flow of individuals that also brings changes in genotype frequencies.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Population Genetics

Effect of Genetic drift: Genetic drift in population can lead to elimination of alleles from that population by chance. In this example, brown coat color allele is dominant over white coat color allele. In the first generation, two alleles occur with equal frequency in the population, resulting in p and q values of. 5 Only half of individuals reproduce, resulting in second generation with p and q values of. 7 and. 3, respectively. Only two individuals in the second generation reproduce and, by chance, these individuals are homozygous dominant for brown coat color. As a result, in the third generation recessive B allele is lose. Genetic drift over time: Ten simulations of random genetic drift of single give allele with initial frequency distribution of 0. 5 measure over the course of 50 generations, repeated in three reproductively synchronous populations of different sizes. In these simulations, alleles drift to loss or fixation only in the smallest population. Effect of population size on Genetic drift: Ten simulations each of random change in frequency distribution of single hypothetical allele over 50 generations for different sized populations; first population size n = 20, second population n = 200, and third population n = 2000.


Genetic Drift

Another scenario in which populations might experience strong influence of genetic drift is if some portion of the population leaves to start a new population in a new location or if the population is divided by physical barrier of some kind. In this situation, it is improbable that those individuals are representative of the entire population, which results in founder effect. Founder effect occurs when genetic structure changes to match that of new populations founding fathers and mothers. The Founder effect is believed to have been a key factor in the genetic history of the Afrikaner population of Dutch settlers in South Africa, as evidenced by mutations that are common in Afrikaners, but rare in most other populations. This was probably due to the fact that a higher - than - normal proportion of founding colonists carried these mutations. As a result, population has unusually high incidences of Huntingtons disease and Fanconi anemia, genetic disorder known to cause blood marrow and congenital abnormalities, even cancer.


Gene Flow and Mutation

Mutations are changes to organisms ' DNA and are an important driver of diversity in populations. Species evolve because of the accumulation of mutations that occur over time. The appearance of new mutations is the most common way to introduce novel genotypic and phenotypic variance. Some mutations are unfavorable or harmful and are quickly eliminated from the population by natural selection. Others are beneficial and will spread through the population. Whether or not mutation is beneficial or harmful is determined by whether it helps organism survive to sexual maturity and reproduce. Some mutations have no effect on organism and can linger, unaffected by natural selection, in the genome, while others can have dramatic effect on genes and resulting phenotype.


Nonrandom Mating and Environmental Variance

If individuals nonrandomly mate with their peers, result could be a changing population. There are many reasons nonrandom mating occurs. One reason is simple mate choice; for example, female peahens may prefer peacocks with bigger, brighter tails. Traits that lead to more matings for individuals become selected for by natural selection. One common form of mate choice, called assortative mating, is individual preference to mate with partners who are phenotypically similar to themselves. 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.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Hardy-Weinberg Principle of Equilibrium

The Hardy - Weinberg principle relates allele frequencies to genotype frequencies in randomly mating population. Imagine that you have a population with two alleles that segregate at a single locus. The frequency of allele is denoted by p and the frequency of allele B is denoted by q. Hardy - Weinberg principle states that after one generation of random mating genotype frequencies will be p 2 2 pq, and q 2. In absence of other evolutionary forces, genotype frequencies are expected to remain constant and population is said to be at Hardy - Weinberg equilibrium. The Hardy - Weinberg principle relies on a number of assumptions: random mating, absence of natural selection, very large population size, no gene flow or migration, no mutation, and locus is autosomal. When these assumptions are violate, departures from Hardy - Weinberg proportions can result. There are a number of evolutionary implications of the Hardy - Weinberg principle. Most importantly, genetic variation is conserved in large, randomly mating populations. The second implication is that the Hardy - Weinberg principle allows one to determine the proportion of individuals that are carriers of recessive allele. Third, it is important to note that dominant alleles are not always the most common alleles in the population. Another implication of the Hardy - Weinberg principle is that rare alleles are more likely to be found in heterozygous individuals than in homozygous individuals. This occurs because q 2 is much smaller than 2 pq when q is close to zero. The Hardy - Weinberg principle can be generalized to include polyploid organisms and genes that have more than two segregating alleles. Equilibrium genotype frequencies are found by expanding multinomial N, where N is number of sets of chromosomes in a cell and k is the number of segregating alleles. For example, tetraploid organisms with two segregating alleles are expected to have genotype frequencies of: p 1 4 4 p 1 3 p 2 6 p 1 2 p 2 2 4 p 1 p 2 3, and p 4. Similarly, diploid organisms with three segregating alleles are expected to have genotype frequencies of: p 1 2, p 2 2, p 3 2 2, p 1 p 2, 2, p 1 p 3, and 2 p 2 p 3. Genotype frequencies sum to one for each of the above scenarios. Although the Hardy - Weinberg principle can also be generalized to include genes located on sex chromosomes, it is important to note that it can take multiple generations for genotype frequencies at sex - link loci to reach equilibrium values. One useful way to think about the Hardy - Weinberg principle is to use the metaphor of gene pool. Here, individuals contribute alleles to an infinitely large pool of games. In randomly mating population without natural selection, offspring genotypes are found by randomly sampling two alleles from this gene pool.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Genetic Drift vs. Natural Selection

Recent debates about random Drift are often entangled with debates over purport purely statistical nature of Evolutionary biology, but issues are separable. There are issues concerning random Drift that do not involve questions of statisticalism, and there are issues concerning statisticalism that do not involve random Drift. Statisticalist claim, generally traced to pair of papers by Walsh, Lewens, and Ariew and Matthen and Ariew, is essentially that evolution is a population - level phenomenon, and that although there are causes at the level of individual organisms, there are no causes at population level, only statistical summary of individual events. Note that it is widely acknowledged that models in Evolutionary Theory are statistical ones, so distinctive statisticalist claim is that Evolutionary biology is purely statistical. There are at least three alternatives to statisticalist claim; one challenges the claim that Evolutionary biology is a population - level phenomenon, arguing that it is constituted by causes at the level of individual organisms,. The second defends the view that there are population - level causes, while the third argues for causes at both levels. It was already noted above that outcome - Only definition of Drift is often adopted by statisticalists, but not exclusively so; it can also be endorse by causalist who, eg, believe that natural selection is a causal process but that Drift is simply a deviation from selective expectations. Perhaps surprisingly, it would also be possible for someone to endorse a version of Causal Process Account of Drift and yet still accept the basic statisticalist premiseif one thought that Drift should be understood in terms of indiscriminate sampling, and also thought that indiscriminate sampling should be understood in terms of causes at level of individual organisms, then Evolutionary changes work by Drift would just be be statistical summation of individual level causes. In short, it would be a mistake to infer one position on statisticalist Debate from one definition of Drift, although such slippage is common and issues are in truth often entangle. What, then, are statisticalist issues that random Drift is entangled with? Concerns raised by Walsh, Lewens, and Ariew and Matthen and Ariew have their origins in claims made by Sober in his classic Nature of Selection. Sober characterizes Evolutionary Theory as Theory of forces, with its Zero - Force state described by Hardy - Weinberg equation of population Genetics; In such a state, there is no selection, no mutation, no migration, no meiotic drive, random mating, and infinite population size. Thus, Hardy - Weinberg equation is an idealized model that never obtained in the real world. It is a bit difficult to see where Drift fits into the equation, which is no doubt the source of much of the confusion over how to define Drift. In his 1984 book, Sober alternatively characterizes Drift in terms of random sampling and sampling error.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Drift and fixation

Genetic drift acts in all populations, and so stochastic effects of finite population size can play a role in large populations as well. Under Hill - Robertson interference, genetic linkage is seen to increase the amount of genetic drift near select locus, thus reducing effective population size for locus when either beneficial mutation arises or in the presence of purifying selection against deleterious allele. Keightley and Otto contrast the probability of fixation for allele modifying recombination with neutral allele, and show that purifying selection against repeat deleterious mutations provides an advantage to modifier alleles, causing them to fix with higher probability. Surprisingly, this effect increases with increasing population size. To understand this somewhat counter - intuitive result, we note that recombination frees focal locus from Hill - Robertson interference, allowing deleterious mutations to be purged by selection. A larger number of polymorphic loci increases the opportunity for Hill - Robertson interference, which increases the advantage for recombination. Larger populations will maintain greater polymorphism, and thus see on average greater amount of Hill - Robertson interference, and larger advantage to recombination. The Keightley - Otto model gives truly synthetic treatment of the role of negative disequilibrium where both selection and drift determine how selection on new mutation affects the fate of other loci, and recombination frees loci from these shared fates.


Measuring Genetic Drift

Genetic drift means change in gene pool strictly by chance fixation of alleles. The effects of genetic drift can be acute in small populations and for infrequently occurring alleles, which can suddenly increase in frequency in the population or be totally wiped out. Alleles thus fixed by chance may be neutralthat is, they may not confer any survival or reproductive advantage. Therefore, for small populations, genetic drift can result in significant change in gene frequency in a short period of time. Genetic drift can be caused by a number of chance phenomena, such as differential number of offspring left by different members of the population so that certain genes increase or decrease in number over generations independent of selection, sudden immigration or emigration of individuals in the population, changing gene frequency in the resulting population, or population bottleneck. Of these, population bottlenecks can cause radical change in allele frequencies in very short time. Population bottlenecks occur when populations suddenly shrink in size owing to random events, such as sudden death of individuals due to environmental catastrophe, habitat destruction, predation, or hunting. When a small number of surviving individuals give rise to a new population, there is a radical change in gene frequency in the resulting population, in which certain genes of the original population may radically increase in proportion while others may radically decrease or be wiped out completely, independently of selection. Additionally, resulting population contains a small fraction of the genetic diversity of the original population. Founder effect is a severe case of population bottlenecking and it happens when few individuals migrate out of the population to establish new subpopulation. Random genetic drift accompanies such founder effect, to severely reduce genetic variation that exist in the original population. In new population, founder effect can rapidly increase the frequency of allele whose frequency was very low in the original population. If allele is a disease - related allele, founder effect can lead to prevalence of disease in new population. An increase in specific diseases in the human population due to founder effect is seen in Old Order Amish of eastern Pennsylvania, 66 and in the Afrikaner population of South Africa. 67 current Amish population has descended from a small number of German immigrants who settled in the United States during the eighteenth century. The incidence of Ellis - van Creveld syndrome is many times more prevalent in this Amish population than in the American population in general. The origin of this disease can be traced back to one couple, Samuel King and his wife, who came to the area in 1744. A mutated gene that causes syndrome was passed along from the Kings and their offspring. The Amish population practices endogamy. Additionally, in this community, gene flow is centrifugal. That is, members may leave the community but outsiders do not join the communitytherefore,. There has been no introduction of exogenous genes into the Amish gene pool.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Genetic Drift Examples

Genetic drift is change in allele frequencies in the population over time due to random sampling events. Although specific genetic consequences of genetic drift during give demographic bottleneck are unpredictable, overall effect of drift is to erode genetic diversity. Effective population size, or N e, is a measure of how sensitive a population is to genetic drift. N e is defined as the size of a hypothetical, theoretically ideal population that would experience the same level of inbreeding, loss of heterozygosity, and genetic drift per generation as the real population in question. Other factors besides census size of population will influence changes in allele frequencies over time; by excluding these factors, N e make it possible to evaluate and compare measurements of drift across species with very different life histories. There are different ways to empirically estimate N e over both short - and long - term time scales, but N e is virtually always smaller, and often much smaller, than the census size of the population. The Frankham review published estimates of N e / N for wildlife species, and found that N e averages only 10 - 11% of total census size. In large populations, it takes a long time to see the major effect of genetic drift on allele frequencies; genetic diversity represents a balance between mutation and natural selection. However, when N e s < 1, where s is selection coefficient describing difference in fitness between two alleles, drift can counter selection, and alleles will behave as if they are neutral. Thus, through this mechanism, small populations may show greater maladaptation than larger ones. By similar logic, mildly deleterious mutations will tend to accumulate in small populations, because selection is ineffective at removing them. This can lead to mutational meltdown: as deleterious mutations become fix, they drive down the population growth rate, making the population progressively more susceptible to fixation of future mutations.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Types of Genetic Drift

Population bottleneck is a type of genetic drift in which population size severely decrease. Competition, disease, or predation lead to these massive decreases in population size. Allele pool is now determined by organisms which do not die. Some alleles increase in frequency simply because they are only alleles left. This type of genetic drift can be seen when people do take their entire course of antibiotics. Antibiotics kill harmful bacteria in your system, regardless of what alleles they have. Antibiotics cause a massive reduction in harmful bacteria. This stops symptoms of disease. A small population will survive if patients quit their antibiotics early. This much smaller population could have allele frequencies that are very different from the original population of bacteria. These changes do not reflect success or failure of different alleles, but rather effects of random selection of bacteria. New alleles will dominate the population until selection or more genetic drift cause allele frequencies to change.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Sources

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

logo

Plex.page is an Online Knowledge, where all the summaries are written by a machine. We aim to collect all the knowledge the World Wide Web has to offer.

Partners:
Nvidia inception logo

© All rights reserved
2021 made by Algoritmi Vision Inc.

If you believe that any of the summaries on our website lead to misinformation, don't hesitate to contact us. We will immediately review it and remove the summaries if necessary.

If your domain is listed as one of the sources on any summary, you can consider participating in the "Online Knowledge" program, if you want to proceed, please follow these instructions to apply.
However, if you still want us to remove all links leading to your domain from Plex.page and never use your website as a source, please follow these instructions.