New Alleles Can Be Created in All of the Following Ways, Except by

Genetic Variation

Genetic variation is a measure of the variation that exists in the genetic makeup of individuals within population.

Learning Objectives

Assess the ways in which genetic variance affects the evolution of populations

Cardinal Takeaways

Key Points

• Genetic variation is an important strength in evolution as information technology allows natural selection to increment or subtract frequency of alleles already in the population.
• Genetic variation tin be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination betwixt homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).
• Genetic variation is advantageous to a population because it enables some individuals to arrange to the surround while maintaining the survival of the population.

Key Terms

• genetic variety: the level of biodiversity, refers to the full number of genetic characteristics in the genetic makeup of a species
• crossing over: the commutation of genetic textile between homologous chromosomes that results in recombinant chromosomes
• phenotypic variation: variation (due to underlying heritable genetic variation); a fundamental prerequisite for evolution past 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. The genetic variation of an entire species is frequently called genetic diversity. Genetic variations are the differences in DNA segments or genes between individuals and each variation of a gene is called an allele.For case, a population with many unlike alleles at a single chromosome locus has a loftier amount of genetic variation. Genetic variation is essential for natural pick because natural choice can only increase or subtract frequency of alleles that already exist in the population.

Genetic variation is caused past:

• mutation
• random mating between organisms
• random fertilization
• crossing over (or recombination) between chromatids of homologous chromosomes during meiosis

The last iii of these factors reshuffle alleles within a population, giving offspring combinations which differ from their parents and from others.

Genetic variation in the shells of Donax variabilis: An enormous amount of phenotypic variation exists in the shells of Donax varabilis, otherwise known as the coquina mollusc. This phenotypic variation is due at to the lowest degree partly to genetic variation inside the coquina population.

Evolution and Adaptation to the Surroundings

Variation allows some individuals within a population to adapt to the changing surroundings. Considering natural selection acts directly only on phenotypes, more genetic variation within a population usually enables more phenotypic variation. Some new alleles increase an organism'southward power to survive and reproduce, which so ensures the survival of the allele in the population. Other new alleles may be immediately detrimental (such as a malformed oxygen-carrying protein) and organisms carrying these new mutations will die out. Neutral alleles are neither selected for nor against and usually remain in the population. Genetic variation is advantageous because it enables some individuals and, therefore, a population, to survive despite a irresolute environment.

Low genetic variety in the wild cheetah population: Populations of wild cheetahs have very low genetic variation. Because wild cheetahs are threatened, their species has a very low genetic diversity. This depression genetic diversity means they are often susceptible to disease and oftentimes laissez passer on lethal recessive mutations; but about v% of cheetahs survive to adulthood.

Geographic Variation

Some species display geographic variation besides as variation inside a population. Geographic variation, or the distinctions in the genetic makeup of different populations, often occurs when populations are geographically separated by environmental barriers or when they are under pick pressures from a dissimilar environment. One example of geographic variation are clines: graded changes in a character down a geographic axis.

Sources of Genetic Variation

Gene duplication, mutation, or other processes can produce new genes and alleles and increase genetic variation. New genetic variation tin be created within generations in a population, then a population with rapid reproduction rates will probably have high genetic variation. Withal, existing genes can be arranged in new ways from chromosomal crossing over and recombination in sexual reproduction. Overall, the principal sources of genetic variation are the formation of new alleles, the altering of gene number or position, rapid reproduction, and sexual reproduction.

Genetic Drift

Genetic drift is the alter in allele frequencies of a population due to random gamble events, such as natural disasters.

Learning Objectives

Distinguish between selection and genetic migrate

Fundamental Takeaways

Key Points

• Genetic drift is the modify in the frequency of an allele in a population due to random sampling and the random events that influence the survival and reproduction of those individuals.
• The bottleneck effect occurs when a natural disaster or similar event randomly kills a large portion (i.east. random sample) of the population, leaving survivors that have allele frequencies that were very different from the previous population.
• The founder effect occurs when a portion of the population (i.e. "founders") separates from the old population to start a new population with different allele frequencies.
• Small populations are more susceptible genetic drift than large populations, whose larger numbers tin can buffer the population confronting adventure events.

Key Terms

• genetic migrate: an overall shift of allele distribution in an isolated population, due to random sampling
• founder consequence: a decrease in genetic variation that occurs when an entire population descends from a small number of founders
• random sampling: a subset of individuals (a sample) chosen from a larger set (a population) by chance

Genetic Drift vs. Natural Selection

Genetic migrate is the converse of natural option. The theory of natural option maintains that some individuals in a population have traits that enable to survive and produce more offspring, while other individuals take traits that are detrimental and may cause them to die earlier reproducing. Over successive generation, these selection pressures tin can change the factor pool and the traits inside the population. For instance, a big, powerful male gorilla will mate with more than females than a small, weak male and therefore more of his genes will be passed on to the next generation. His offspring may continue to dominate the troop and pass on their genes as well. Over time, the selection pressure will cause the allele frequencies in the gorilla population to shift toward large, strong males.

Unlike natural choice, genetic migrate describes the upshot of chance on populations in the absence of positive or negative choice pressure level. Through random sampling, or the survival or and reproduction of a random sample of individuals within a population, allele frequencies within a population may modify. Rather than a male gorilla producing more offspring because he is stronger, he may be the only male bachelor when a female person is ready to mate. His genes are passed on to time to come generation because of adventure, not considering he was the biggest or the strongest. Genetic drift is the shift of alleles within a population due to chance events that cause random samples of the population to reproduce or not.

Effect of genetic drift: Genetic drift in a population can lead to the elimination of an allele from that population by gamble. In this example, the brown coat color allele (B) is ascendant over the white coat colour allele (b). In the first generation, the 2 alleles occur with equal frequency in the population, resulting in p and q values of.five. But one-half of the individuals reproduce, resulting in a second generation with p and q values of.7 and.three, respectively. Only 2 individuals in the second generation reproduce and, by chance, these individuals are homozygous dominant for dark-brown coat color. Every bit a upshot, in the 3rd generation the recessive b allele is lost.

Small populations are more susceptible to the forces of genetic drift. Big populations, on the other hand, are buffered against the effects of take a chance. If ane individual of a population of x individuals happens to dice at a young historic period before leaving whatever offspring to the side by side generation, all of its genes (ane/ten of the population's gene pool) will be all of a sudden lost. In a population of 100, that individual represents only 1 percent of the overall genetic pool; therefore, genetic drift has much less touch on the larger population's genetic structure.

The Clogging Effect

Genetic migrate can also be magnified by natural events, such as a natural disaster that kills a large portion of the population at random. The bottleneck consequence occurs when but 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.

Effect of a bottleneck on a population: A chance upshot or catastrophe can reduce the genetic variability within a population.

The Founder Effect

Another scenario in which populations might feel a strong influence of genetic drift is if some portion of the population leaves to start a new population in a new location or if a population gets divided past a concrete barrier of some kind. In this situation, it is improbable that those individuals are representative of the unabridged population, which results in the founder effect. The founder event occurs when the genetic structure changes to lucifer that of the new population's founding fathers and mothers.

The Founder Effect: The founder consequence occurs when a portion of the population (i.e. "founders") separates from the old population to commencement a new population with dissimilar allele frequencies.

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, merely rare in most other populations. This was probably due to the fact that a higher-than-normal proportion of the founding colonists carried these mutations. As a result, the population expresses unusually high incidences of Huntington's disease (Hd) and Fanconi anemia (FA), a genetic disorder known to crusade blood marrow and built abnormalities, even cancer.

Drift and fixation

The Hardy–Weinberg principle states that within sufficiently big populations, the allele frequencies remain constant from ane generation to the adjacent unless the equilibrium is disturbed by migration, genetic mutation, or selection.

Considering the random sampling tin can remove, simply non supercede, an allele, and because random declines or increases in allele frequency influence expected allele distributions for the next generation, genetic drift drives a population towards genetic uniformity over time. When an allele reaches a frequency of 1 (100%) it is said to be "fixed" in the population and when an allele reaches a frequency of 0 (0%) it is lost. Once an allele becomes fixed, genetic drift for that allele comes to a halt, and the allele frequency cannot change unless a new allele is introduced in the population via mutation or factor flow. Thus even while genetic drift is a random, directionless process, it acts to eliminate genetic variation over time.

Genetic migrate over time: Ten simulations of random genetic drift of a single given allele with an initial frequency distribution 0.five measured over the course of fifty generations, repeated in 3 reproductively synchronous populations of different sizes. In these simulations, alleles drift to loss or fixation (frequency of 0.0 or i.0) just in the smallest population.Effect of population size on genetic drift: Ten simulations each of random modify in the frequency distribution of a unmarried hypothetical allele over 50 generations for different sized populations; first population size n=20, second population north=200, and third population n=2000.

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.

Learning Objectives

Explicate how gene menstruation and mutations tin can influence the allele frequencies of a population

Central Takeaways

Fundamental Points

• Found populations experience gene flow by spreading their pollen long distances.
• Animals feel cistron flow when individuals leave a family group or herd to join other populations.
• The flow of individuals in and out of a population introduces new alleles and increases genetic variation within that population.
• Mutations are changes to an organism's DNA that create diverseness within a population by introducing new alleles.
• Some mutations are harmful and are quickly eliminated from the population past natural selection; harmful mutations prevent organisms from reaching sexual maturity and reproducing.
• Other mutations are beneficial and can increase in a population if they help organisms achieve sexual maturity and reproduce.

Central Terms

• cistron flow: the transfer of alleles or genes from one population to another
• mutation: whatever heritable change of the base-pair sequence of genetic material

Cistron Menstruation

An important evolutionary strength is gene flow: the flow of alleles in and out of a population due to the migration of individuals or gametes. While some populations are fairly stable, others experience more movement and fluctuation. Many plants, for example, ship their pollen past wind, insects, or birds to pollinate other populations of the same species some distance away. Even a population that may initially appear to exist stable, such every bit a pride of lions, can receive new genetic variation as developing males get out their mothers to form new prides with genetically-unrelated females. This variable flow of individuals in and out of the grouping not only changes the gene structure of the population, merely can likewise innovate new genetic variation to populations in different geological locations and habitats.

Gene flow: Gene flow can occur when an individual travels from ane geographic location to another.

Maintained gene flow betwixt two populations can as well lead to a combination of the two gene pools, reducing the genetic variation between the two groups. Gene flow strongly acts against speciation, past recombining the gene pools of the groups, and thus, repairing the developing differences in genetic variation that would have led to full speciation and creation of daughter species.

For instance, if a species of grass grows on both sides of a highway, pollen is probable to be transported from one side to the other and vice versa. If this pollen is able to fertilize the plant where it ends upward and produce feasible offspring, then the alleles in the pollen have finer linked the population on ane side of the highway with the other.

Mutation

Mutations are changes to an organism's Deoxyribonucleic acid and are an important commuter of diversity in populations. Species evolve because of the accumulation of mutations that occur over fourth dimension. The advent of new mutations is the most common fashion 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 a mutation is benign or harmful is determined by whether it helps an organism survive to sexual maturity and reproduce. Some mutations accept no effect on an organism and can linger, unaffected past natural pick, in the genome while others can have a dramatic event on a gene and the resulting phenotype.

Mutation in a garden rose: A mutation has caused this garden moss rose to produce flowers of unlike colors. This mutation has innovate a new allele into the population that increases genetic variation and may be passed on to the next generation.

Nonrandom Mating and Environmental Variance

Population construction can be altered by nonrandom mating (the preference of sure individuals for mates) as well every bit the environs.

Learning Objectives

Explain how environmental variance and nonrandom mating tin can alter gene frequencies in a population

Key Takeaways

Key Points

• Nonrandom mating can occur when individuals prefer mates with item superior physical characteristics or by the preference of individuals to mate with individuals similar to themselves.
• Nonrandom mating can also occur when mates are called based on physical accessibility; that is, the availability of some mates over others.
• Phenotypes of individuals can too be influenced by the environs in which they live, such as temperature, terrain, or other factors.
• A cline occurs when populations of a given species vary gradually across an ecological gradient.

Cardinal Terms

• cline: a gradation in a character or phenotype inside a species or other group
• sexual selection: a style of natural selection in which some individuals out-reproduce others of a population considering they are improve at securing mates
• assortative mating: between males and females of a species, the common attraction or choice, for reproductive purposes, of individuals with like characteristics

Nonrandom Mating

If individuals nonrandomly mate with other individuals in the population, i.east. they choose their mate, choices can bulldoze evolution within a population. There are many reasons nonrandom mating occurs. One reason is simple mate choice or sexual selection; for case, female person peahens may adopt peacocks with bigger, brighter tails. Traits that atomic number 82 to more matings for an private atomic number 82 to more offspring and through natural selection, eventually lead to a college frequency of that trait in the population. I mutual form of mate choice, called positive assortative mating, is an individual'south preference to mate with partners that are phenotypically similar to themselves.

Assortative mating in the American Robin: The American Robin may practice assortative mating on plumage color, a melanin based trait, and mate with other robins who have the most similar shade of colour. Yet, there may also be some sexual choice for more vibrant plumage which indicates health and reproductive operation.

Some other crusade of nonrandom mating is physical location. This is particularly truthful in large populations spread over big geographic distances where non all individuals volition take equal access to i another. Some might exist miles apart through woods or over rough terrain, while others might alive immediately nearby.

Environmental Variance

Genes are not the just players involved in determining population variation. Phenotypes are also influenced by other factors, such as the environment. A beachgoer is likely to accept darker skin than a urban center dweller, for example, due to regular exposure to the sun, an environmental factor. Some major characteristics, such as gender, are determined by the environment for some species. For case, some turtles and other reptiles take temperature-dependent sex determination (TSD). TSD means that individuals develop into males if their eggs are incubated inside a certain temperature range, or females at a different temperature range.

Temperature-dependent sex decision: The sexual practice of the American alligator (Alligator mississippiensis) is determined by the temperature at which the eggs are incubated. Eggs incubated at 30 degrees C produce females, and eggs incubated at 33 degrees C produce males.

Geographic separation between populations can lead to differences in the phenotypic variation betwixt those populations. Such geographical variation is seen betwixt most populations and can be significant. One type of geographic variation, chosen a cline, can be seen as populations of a given species vary gradually beyond an ecological slope.

Geographic variation in moose: This graph shows geographical variation in moose; body mass increment positively with latitude. Bergmann's Rule is an ecologic principle which states that every bit latitude increases the body mass of a item species increases. The data are taken from a Swedish study investigating the size of moose as latitude increases every bit shows the positive relationship betwixt the two, supporting Bergmann's Dominion.

Species of warm-blooded animals, for example, tend to take larger bodies in the cooler climates closer to the earth'due south poles, allowing them to better conserve heat. This is considered a latitudinal cline. Alternatively, flowering plants tend to flower at different times depending on where they are along the slope of a mountain, known as an altitudinal cline.

If there is cistron menses between the populations, the individuals will likely testify gradual differences in phenotype along the cline. Restricted gene catamenia, on the other mitt, can pb to abrupt differences, even speciation.

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Source: https://courses.lumenlearning.com/boundless-biology/chapter/population-genetics/

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