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Genetic Load
Genetic load is the difference between the fitness of an average genotype in a population and the fitness of some reference genotype, which may be either the best present in a population, or may be the theoretically optimal genotype. The average individual taken from a population with a low genetic load will generally, when grown in the same conditions, have more surviving offspring than the average individual from a population with a high genetic load. Genetic load can also be seen as reduced fitness at the population level compared to what the population would have if all individuals had the reference high-fitness genotype. High genetic load may put a population in danger of extinction. Fundamentals Consider n genotypes \mathbf _1, \dots, \mathbf _n, which have the fitnesses w_1, \dots, w_n and frequencies p_1, \dots, p_n, respectively. Ignoring frequency-dependent selection, the genetic load L may be calculated as: :L = where w_\max is either some theoretical optimum, or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fitness (biology)
Fitness (often denoted w or ω in population genetics models) is a quantitative representation of individual reproductive success. It is also equal to the average contribution to the gene pool of the next generation, made by the same individuals of the specified genotype or phenotype. Fitness can be defined either with respect to a genotype or to a phenotype in a given environment or time. The fitness of a genotype is manifested through its phenotype, which is also affected by the developmental environment. The fitness of a given phenotype can also be different in different selective environments. With asexual reproduction, it is sufficient to assign fitnesses to genotypes. With sexual reproduction, recombination scrambles alleles into different genotypes every generation; in this case, fitness values can be assigned to alleles by averaging over possible genetic backgrounds. Natural selection tends to make alleles with higher fitness more common over time, resulting in Darwini ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Genetic Drift
Genetic drift, also known as random genetic drift, allelic drift or the Wright effect, is the change in the Allele frequency, frequency of an existing gene variant (allele) in a population due to random chance. Genetic drift may cause gene variants to disappear completely and thereby reduce genetic variation. It can also cause initially rare alleles to become much more frequent and even fixed. When few copies of an allele exist, the effect of genetic drift is more notable, and when many copies exist, the effect is less notable (due to the law of large numbers). In the middle of the 20th century, vigorous debates occurred over the relative importance of natural selection versus neutral processes, including genetic drift. Ronald Fisher, who explained natural selection using Mendelian inheritance, Mendelian genetics, held the view that genetic drift plays at most a minor role in evolution, and this remained the dominant view for several decades. In 1968, population geneticist Mot ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alexey Kondrashov
Alexey Simonovich Kondrashov () (born April 11, 1957) worked on a variety of subjects in evolutionary genetics. He is best known for the ''deterministic mutation hypothesis''Kondrashov, A.S. 1988. Deleterious mutations and the evolution of sexual reproduction. ''Nature'' 336: 435-440 explaining the maintenance of sexual reproduction,Kondrashov AS & Crow JF. 1991. Haploidy or diploidy: which is better? ''Nature'' 351:314-315 his work on sympatric speciation,Kondrashov AS & Kondrashov FA. 1999. Interactions among quantitative traits in the course of symaptric speciation. ''Nature'' 400: 351-354 and his work on evaluating mutation rates.Kondrashov AS & Houle D. 1994. Genotype-Environment interactions and the estimation of the genomci mutation-reate in ''Drosophila melanogaster''. '' Proceedings of the Royal Society of London Series B-Biological Sciences'' 258: 221-227 Originally from the Soviet Union, A.S. Kondrashov has been working in the United States since the early 1990s. His ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
James F
James may refer to: People * James (given name) * James (surname) * James (musician), aka Faruq Mahfuz Anam James, (born 1964), Bollywood musician * James, brother of Jesus * King James (other), various kings named James * Prince James (other) * Saint James (other) Places Canada * James Bay, a large body of water * James, Ontario United Kingdom * James College, a college of the University of York United States * James, Georgia, an unincorporated community * James, Iowa, an unincorporated community * James City, North Carolina * James City County, Virginia ** James City (Virginia Company) ** James City Shire * James City, Pennsylvania * St. James City, Florida Film and television * ''James'' (2005 film), a Bollywood film * ''James'' (2008 film), an Irish short film * ''James'' (2022 film), an Indian Kannada-language film * "James", a television episode of ''Adventure Time'' Music * James (band), a band from Manchester ** ''James'', ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hermann Joseph Muller
Hermann Joseph Muller (December 21, 1890 – April 5, 1967) was an American geneticist who was awarded the 1946 Nobel Prize in Physiology or Medicine, "for the discovery that mutations can be induced by X-rays". Muller warned of long-term dangers of radioactive fallout from nuclear war and nuclear testing, which resulted in greater public scrutiny of these practices. Early life Muller was born in New York City, the son of Frances (Lyons) and Hermann Joseph Muller Sr., an artisan who worked with metals. Muller was a third-generation American whose father's ancestors were originally Catholic and came to the United States from Koblenz. His mother's family was of mixed Jewish (descended from Spanish and Portuguese Jews) and Anglican background, and had come from Britain. Among his first cousins was Alfred Kroeber (Kroeber was Ursula Le Guin's father) and first cousins once removed was Herbert J. Muller. As an adolescent, Muller attended a Unitarian church and considered himsel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mutational Meltdown
In evolutionary genetics, mutational meltdown is a sub class of extinction vortex in which the environment and genetic predisposition mutually reinforce each other. Mutational meltdown (not to be confused with the concept of an error catastrophe) is the accumulation of harmful mutations in a small population, which leads to loss of fitness and decline of the population size, which may lead to further accumulation of deleterious mutations due to fixation by genetic drift. This loss of fitness is drift load, and it is a target of conservation genetics. A population experiencing mutational meltdown is trapped in a downward spiral and will go extinct if the phenomenon lasts for some time. Usually, the deleterious mutations would simply be selected away, but during a mutational meltdown, the number of individuals not reproducing (e.g. by suffering an early death) is too large relative to the overall population size so that mortality exceeds the birth rate. Explanation ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Small Population Size
Small populations can behave differently from larger populations. They are often the result of population bottlenecks from larger populations, leading to loss of heterozygosity and reduced genetic diversity and loss or fixation of alleles and shifts in allele frequencies. A small population is then more susceptible to demographic and genetic stochastic events, which can impact the long-term survival of the population. Therefore, small populations are often considered at risk of endangerment or extinction, and are often of conservation concern. Demographic effects The influence of stochastic variation in demographic (reproductive and mortality) rates is much higher for small populations than large ones. Stochastic variation in demographic rates causes small populations to fluctuate randomly in size. This variation could be a result of unequal sex ratios, high variance in family size, inbreeding, or fluctuating population size.Frankham, R., Briscoe, D. A., & Ballou, J. D. (2002). ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Epistasis
Epistasis is a phenomenon in genetics in which the effect of a gene mutation is dependent on the presence or absence of mutations in one or more other genes, respectively termed modifier genes. In other words, the effect of the mutation is dependent on the genetic background in which it appears. Epistatic mutations therefore have different effects on their own than when they occur together. Originally, the term ''epistasis'' specifically meant that the effect of a gene variant is masked by that of different gene. The concept of ''epistasis'' originated in genetics in 1907 but is now used in biochemistry, computational biology and evolutionary biology. The phenomenon arises due to interactions, either between genes (such as mutations also being needed in regulators of gene expression) or within them (multiple mutations being needed before the gene loses function), leading to non-linear effects. Epistasis has a great influence on the shape of evolutionary landscapes, which leads ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Evolution Of Sexual Reproduction
Sexually reproducing animals, plants, fungi and protists are thought to have evolved from a common ancestor that was a single-celled eukaryotic species. Sexual reproduction is widespread in eukaryotes, though a few eukaryotic species have secondarily lost the ability to reproduce sexually, such as Bdelloidea, and some plants and animals routinely reproduce asexually (by apomixis and parthenogenesis) without entirely having lost sex. The evolution of sexual reproduction contains two related yet distinct themes: its ''origin'' and its ''maintenance.'' Bacteria and Archaea (prokaryotes) have processes that can transfer DNA from one cell to another (conjugation, transformation, and transduction), but it is unclear if these processes are evolutionarily related to sexual reproduction in Eukaryotes. In eukaryotes, true sexual reproduction by meiosis and cell fusion is thought to have arisen in the last eukaryotic common ancestor, possibly via several processes of varying suc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nature (journal)
''Nature'' is a British weekly scientific journal founded and based in London, England. As a multidisciplinary publication, ''Nature'' features Peer review, peer-reviewed research from a variety of academic disciplines, mainly in science and technology. It has core editorial offices across the United States, continental Europe, and Asia under the international scientific publishing company Springer Nature. ''Nature'' was one of the world's most cited scientific journals by the Science Edition of the 2022 ''Journal Citation Reports'' (with an ascribed impact factor of 50.5), making it one of the world's most-read and most prestigious academic journals. , it claimed an online readership of about three million unique readers per month. Founded in the autumn of 1869, ''Nature'' was first circulated by Norman Lockyer and Alexander MacMillan (publisher), Alexander MacMillan as a public forum for scientific innovations. The mid-20th century facilitated an editorial expansion for the j ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Genetic Recombination
Genetic recombination (also known as genetic reshuffling) is the exchange of genetic material between different organisms which leads to production of offspring with combinations of traits that differ from those found in either parent. In eukaryotes, genetic recombination during meiosis can lead to a novel set of genetic information that can be further passed on from parents to offspring. Most recombination occurs naturally and can be classified into two types: (1) ''interchromosomal'' recombination, occurring through independent assortment of alleles whose loci are on different but homologous chromosomes (random orientation of pairs of homologous chromosomes in meiosis I); & (2) ''intrachromosomal'' recombination, occurring through crossing over. During meiosis in eukaryotes, genetic recombination involves the pairing of homologous chromosomes. This may be followed by information transfer between the chromosomes. The information transfer may occur without physical exchange (a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Muller's Ratchet
In evolutionary genetics, Muller's ratchet (named after Hermann Joseph Muller, by analogy with a ratchet effect) is a process which, in the absence of recombination (especially in an asexual population), results in an accumulation of irreversible deleterious mutations. (original paper as cited by, e.g.: ; ) This happens because in the absence of recombination, and assuming reverse mutations are rare, offspring bear at least as much mutational load as their parents. Muller proposed this mechanism as one reason why sexual reproduction may be favored over asexual reproduction, as sexual organisms benefit from recombination and consequent elimination of deleterious mutations. The negative effect of accumulating irreversible deleterious mutations may not be prevalent in organisms which, while they reproduce asexually, also undergo other forms of recombination. This effect has also been observed in those regions of the genomes of sexual organisms that do not undergo recombination. Et ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
