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Balancing Selection
Balancing selection refers to a number of selective processes by which multiple alleles (different versions of a gene) are actively maintained in the gene pool of a population at frequencies larger than expected from genetic drift alone. Balancing selection is rare compared to purifying selection. It can occur by various mechanisms, in particular, when the heterozygotes for the alleles under consideration have a higher fitness than the homozygote. In this way genetic polymorphism is conserved. Evidence for balancing selection can be found in the number of alleles in a population which are maintained above mutation rate frequencies. All modern research has shown that this significant genetic variation is ubiquitous in panmictic populations. There are several mechanisms (which are not exclusive within any given population) by which balancing selection works to maintain polymorphism. The two major and most studied are heterozygote advantage and frequency-dependent selection. Mech ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Natural Selection
Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Charles Darwin popularised the term "natural selection", contrasting it with selective breeding, artificial selection, which in his view is intentional, whereas natural selection is not. Genetic diversity, Variation exists within all populations of organisms. This occurs partly because random mutations arise in the genome of an individual organism, and their offspring can inherit such mutations. Throughout the lives of the individuals, their genomes interact with their environments to cause variations in traits. The environment of a genome includes the molecular biology in the Cell (biology), cell, other cells, other individuals, populations, species, as well as the abiotic environment. Because individuals with certain variants of the trait tend ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Red Blood Cells
Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek language, Greek ''erythros'' for "red" and ''kytos'' for "hollow vessel", with ''-cyte'' translated as "cell" in modern usage), are the most common type of blood cell and the vertebrate's principal means of delivering oxygen (O2) to the body tissue (biology), tissues—via blood flow through the circulatory system. RBCs take up oxygen in the lungs, or in fish the gills, and release it into tissues while squeezing through the body's capillary, capillaries. The cytoplasm of a red blood cell is rich in hemoglobin, an iron-containing biomolecule that can bind oxygen and is responsible for the red color of the cells and the blood. Each human red blood cell contains approximately 270 million hemoglobin molecules. The cell membrane is composed of proteins and lipids, and this structure ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Apostatic Selection
Apostatic selection is a form of negative frequency-dependent selection. It describes the survival of individual prey animals that are different (through mutation) from their species in a way that makes it more likely for them to be ignored by their predators. It operates on polymorphic species, species which have different forms. In apostatic selection, the common forms of a species are preyed on more than the rarer forms, giving the rare forms a selective advantage in the population. It has also been discussed that apostatic selection acts to stabilize prey polymorphisms. The term "apostatic selection" was introduced in 1962 by Bryan Clarke in reference to predation on polymorphic grove snails and since then it has been used as a synonym for negative frequency-dependent selection. The behavioural basis of apostatic selection was initially neglected, but was eventually established by A.B Bond. Apostatic selection can also apply to the predator if the predator has various morp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cepaea Nemoralis Active Pair On Tree Trunk
''Cepaea'' is a genus of medium-sized air-breathing land snails, terrestrial pulmonate gastropod mollusks in the family Helicidae. The shells of species within this genus are often brightly colored and patterned with stripes. The two species from this genus, the common and widespread ''C. nemoralis'' and ''C. hortensis'', have been model species for early studies of genetics and natural selection. They occur in Europe, although introduced populations occur elsewhere in the world. Like many Helicidae, this genus of snails create and use love darts. Species For a long time, four species were classified in the genus ''Cepaea''. However, molecular phylogenetic studies suggested that the latter two should be placed in the unrelated genera ''Macularia'' and ''Caucasotachea'': * ''Cepaea hortensis'' (O. F. Müller, 1774) – white-lipped snail or garden banded snail * ''Cepaea nemoralis'' (Linnaeus, 1758) – brown-lipped snail or grove snail * ''Cepaea sylvatica'' (Draparnaud, 1801 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Song Thrush
The song thrush (''Turdus philomelos'') is a Thrush (bird), thrush that breeds across the West Palearctic. It has brown upper-parts and black-spotted cream or buff underparts and has three recognised subspecies. Its distinctive Birdsong, song, which has repeated musical phrases, has frequently been referred to in poetry. The song thrush breeds in forests, gardens and parks, and is partially bird migration, migratory with many birds wintering in southern Europe, North Africa and the Middle East; it has also been introduced into New Zealand and Australia. Although it is not threatened globally, there have been serious population declines in parts of Europe, possibly due to changes in farming practices. The song thrush builds a neat mud-lined bird nest#Cup, cup nest in a bush or tree and lays four to five dark-spotted blue bird egg, eggs. It is omnivorous and has the habit of using a favourite stone as an "anvil" on which to break open the shells of land snail, snails. Like other ... [...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 a 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 l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Multiple Alleles
An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the Locus (genetics), same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chromosomal or genomic location of a gene or any other genetic element is called a locus (plural: loci) and alternative DNA sequences at a locus are called alleles." The simplest alleles are Single-nucleotide polymorphism, single nucleotide polymorphisms (SNP). but they can also be insertions and deletions of up to several thousand base pairs. Popular definitions of 'allele' typically refer only to different alleles within genes. For example, the ABO blood group system, ABO blood grouping is controlled by the ABO (gene), ABO gene, which has six common alleles (variants). In population genetics, nearly every living human's phenotype for the ABO gene is some combination of just these six alleles. Most alleles observed result i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cepaea Nemoralis
The grove snail, brown-lipped snail or Lemon snail (''Cepaea nemoralis'') is a species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ... of air-breathing land snail, a terrestrial molluscs, terrestrial pulmonate gastropod mollusc. MolluscaBase eds. (2020). MolluscaBase. Cepaea nemoralis (Linnaeus, 1758). Accessed through: World Register of Marine Species at: http://marinespecies.org/aphia.php?p=taxdetails&id=235792 on 2020-07-31 It is one of the most common species of land snail in Europe, and has been introduced to North America. ;Subspecies: * ''Cepaea nemoralis etrusca'' (Rossmässler, 1835) * ''Cepaea nemoralis nemoralis'' (Linnaeus, 1758) ''Cepaea nemoralis'' is the type species of the genus ''Cepaea''. It is used as a model organism in citizen science projects. Descriptio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geometric Mean
In mathematics, the geometric mean is a mean or average which indicates a central tendency of a set of numbers by using the product of their values (as opposed to the arithmetic mean which uses their sum). The geometric mean is defined as the th root of the product of numbers, i.e., for a set of numbers , the geometric mean is defined as :\left(\prod_^n a_i\right)^\frac = \sqrt /math> or, equivalently, as the arithmetic mean in logscale: :\exp For instance, the geometric mean of two numbers, say 2 and 8, is just the square root of their product, that is, \sqrt = 4. As another example, the geometric mean of the three numbers 4, 1, and 1/32 is the cube root of their product (1/8), which is 1/2, that is, \sqrt = 1/2. The geometric mean applies only to positive numbers. The geometric mean is often used for a set of numbers whose values are meant to be multiplied together or are exponential in nature, such as a set of growth figures: values of the human population or inter ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Prey Switching
Prey switching is frequency-dependent predation, where the predator preferentially consumes the most common type of prey. The phenomenon has also been described as apostatic selection, however the two terms are generally used to describe different parts of the same phenomenon. Apostatic selection has been used by authors looking at the differences between different genetic morphs. In comparison, prey switching has been used when describing the choice between different species.Allen, J.A. (1988) Frequency-dependent selection by predators. Philos. T. Roy. Soc. B 319, 485-503 Definition The term ''switching'' was first coined by the ecologist Murdoch in 1969 to describe the situation where a predator eats disproportionately more of the most common type of prey. Eight years earlier in 1962 the geneticst B. C. Clarke described a similar phenomenon and called it "apostatic selection". Since then the term ''prey switching'' has mainly been used by ecologists, while ''apostatic selection' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Underdominance
In genetics, underdominance, also known as homozygote advantage, heterozygote disadvantage, or negative overdominance," is the opposite of overdominance. It is the selection against the heterozygote, causing disruptive selection and divergent genotypes. Underdominance exists in situations where the heterozygotic genotype is inferior in fitness to either the dominant or recessive homozygotic genotype. Compared to examples of overdominance in actual populations, underdominance is considered more unstable and may lead to the fixation of either allele. An example of stable underdominance may occur in individuals who are heterozygotic for polymorphisms that would make them better suited for one of two niches. Consider a situation in which a population is completely homozygotic for an "A" allele, allowing exploitation of a particular resource. Eventually, a polymorphic "a" allele may be introduced into the population, resulting in an individual who is capable of exploiting a different ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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