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Chromosome mutations also occur due to changes in chromosome number. This commonly results from chromosome breakage or from the failure of chromosomes to separate correctly nondisjunction during meiosis or mitosis. At Hardy-Weinberg equilibrium, gene flow must not occur in the population. Gene flow , or gene migration occurs when allele frequencies in a population change as organisms migrate into or out of the population. Migration from one population to another introduces new alleles into an existing gene pool through sexual reproduction between members of the two populations.
Gene flow is dependent upon migration between separated populations. Organisms must be able to travel long distances or transverse barriers mountains, oceans, etc. In non-mobile plant populations, such as angiosperms , gene flow may occur as pollen is carried by wind or by animals to distant locations.
Organisms migrating out of a population can also alter gene frequencies. Removal of genes from the gene pool reduces the occurrence of specific alleles and alters their frequency in the gene pool. Immigration brings genetic variation into a population and may help the population to adapt to environmental changes. However, immigration also makes it more difficult for optimal adaptation to occur in a stable environment. The emigration of genes gene flow out of a population could enable adaptation to a local environment, but could also lead to the loss of genetic diversity and possible extinction.
A very large population, one of infinite size , is required for Hardy-Weinberg equilibrium. This condition is needed in order to combat the impact of genetic drift.
Genetic drift is described as a change in the allele frequencies of a population that occurs by chance and not by natural selection. The smaller the population, the greater the impact of genetic drift.
This is because the smaller the population, the more likely that some alleles will become fixed and others will become extinct. Removal of alleles from a population changes allele frequencies in the population.
Allele frequencies are more likely to be maintained in larger populations due to the occurrence of alleles in a large number of individuals in the population. Genetic drift does not result from adaptation but occurs by chance. The alleles that persist in the population may be either helpful or harmful to the organisms in the population. Two types of events promote genetic drift and extremely lower genetic diversity within a population. The first type of event is known as a population bottleneck.
Bottleneck populations result from a population crash that occurs due to some type of catastrophic event that wipes out the majority of the population. The surviving population has limited diversity of alleles and a reduced gene pool from which to draw. A second example of genetic drift is observed in what is known as the founder effect.
In this instance, a small group of individuals become separated from the main population and establish a new population. This colonial group does not have the full allele representation of the original group and will have different allele frequencies in the comparatively smaller gene pool. Random mating is another condition required for Hardy-Weinberg equilibrium in a population. In random mating, individuals mate without preference for selected characteristics in their potential mate.
In order to maintain genetic equilibrium, this mating must also result in the production of the same number of offspring for all females in the population. Non-random mating is commonly observed in nature through sexual selection. In sexual selection , an individual chooses a mate based on traits that are considered to be preferable. Traits, such as brightly colored feathers, brute strength, or large antlers indicate higher fitness. Females, more so than males, are selective when choosing mates in order to improve the chances of survival for their young.
Non-random mating changes allele frequencies in a population as individuals with desired traits are selected for mating more often than those without these traits. In some species , only select individuals get to mate. Over generations, alleles of the selected individuals will occur more often in the population's gene pool.
As such, sexual selection contributes to population evolution. In order for a population to exist in Hardy-Weinberg equilibrium, natural selection must not occur. Natural selection is an important factor in biological evolution. When natural selection occurs, individuals in a population that are best adapted to their environment survive and produce more offspring than individuals that are not as well adapted.
This results in a change in the genetic makeup of a population as more favorable alleles are passed on to the population as a whole. Natural selection changes the allele frequencies in a population. This change is not due to chance, as is the case with genetic drift, but the result of environmental adaptation. The environment establishes which genetic variations are more favorable.
These variations occur as a result of several factors. Gene mutation, gene flow, and genetic recombination during sexual reproduction are all factors that introduce variation and new gene combinations into a population.
Traits favored by natural selection may be determined by a single gene or by many genes polygenic traits. Examples of naturally selected traits include leaf modification in carnivorous plants , leaf resemblance in animals , and adaptive behavior defense mechanisms, such as playing dead.
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The statute is named after G. Hardy and Wilhelm Weinberg. They were leaders in mathematically demonstrating this idea, also known as the Hardy-Weinberg equilibrium, law, model or theorem. Hardy Weinberg principle is a theory which states that in the absence of disrupting factors, genetic diversity in a population would stay constant from one period to the next. In a large population with no destructive conditions, when mating is random, the law assumes that both genotype and allele frequencies will stay constant since they are in balance.
Hardy's work focused on debunking the view that existed in those days that a dominant allele tended to naturally increase in frequency. Below mentioned are the applications of Hardy Weinberg law The confusion over selection and dominance just isn't very exceptional in today's times.
The Hardy-Weinberg genotype frequency tests are currently used to determine population stratification and other forms of non-random mating. Genetic variations that change from mutation, genetic drift, migration, sexual selection and natural selection are persistently reflected by natural populations.
A statistical criterion for a non-evolving population that can be contrasted with evolving populations is given by the Hardy-Weinberg rule. Through this period, if the allele frequencies are recorded and calculated on the basis of the Hardy-Weinberg law values for the predicted frequencies, then it is possible to hypothesize operations that drive population evolution.
The law provides a template that is usually used to research the population genetics of diploid organisms as a point of origin that fulfils the common argument of a large population, random mating, no mutation, selection or migration. However, for haploid pathogens, the Hardy-Weinberg model is not valid.
Each of the principles in this law is thus broken in the case that a population is not discovered in the Hardy Weinberg equilibrium equation. This suggests that the population has been affected by selection, migration or non-random mating, where studies are taken out and theories are pursued in order to understand the mechanism behind its population's non-equilibrium.
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