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Gene Flow
In population genetics, gene flow (also known as gene migration or geneflow and allele flow) is the transfer of genetic material from one population to another. If the rate of gene flow is high enough, then two populations will have equivalent allele frequencies and therefore can be considered a single effective population. It has been shown that it takes only "one migrant per generation" to prevent populations from diverging due to drift. Populations can diverge due to selection even when they are exchanging alleles, if the selection pressure is strong enough. Gene flow is an important mechanism for transferring genetic diversity among populations. Migrants change the distribution of genetic diversity among populations, by modifying allele frequencies (the proportion of members carrying a particular variant of a gene). High rates of gene flow can reduce the genetic differentiation between the two groups, increasing homogeneity. For this reason, gene flow has been thought to c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gene Flow Final
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a basic unit of heredity and the molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protein-coding genes and noncoding genes. During gene expression, the DNA is first copied into RNA. The RNA can be directly functional or be the intermediate template for a protein that performs a function. The transmission of genes to an organism's offspring is the basis of the inheritance of phenotypic traits. These genes make up different DNA sequences called genotypes. Genotypes along with environmental and developmental factors determine what the phenotypes will be. Most biological traits are under the influence of polygenes (many different genes) as well as gene– ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Speciation Modes Edit
Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within lineages. Charles Darwin was the first to describe the role of natural selection in speciation in his 1859 book ''On the Origin of Species''. He also identified sexual selection as a likely mechanism, but found it problematic. There are four geographic modes of speciation in nature, based on the extent to which speciating populations are isolated from one another: allopatric, peripatric, parapatric, and sympatric. Speciation may also be induced artificially, through animal husbandry, agriculture, or laboratory experiments. Whether genetic drift is a minor or major contributor to speciation is the subject of much ongoing discussion. Rapid sympatric speciation can take place through polyploidy, such as by doubling of chromosome number; t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mallard
The mallard () or wild duck (''Anas platyrhynchos'') is a dabbling duck that breeds throughout the temperate and subtropical Americas, Eurasia, and North Africa, and has been introduced to New Zealand, Australia, Peru, Brazil, Uruguay, Argentina, Chile, Colombia, the Falkland Islands, and South Africa. This duck belongs to the subfamily Anatinae of the waterfowl family Anatidae. Males have purple patches on their wings, while the females (hens or ducks) have mainly brown-speckled plumage. Both sexes have an area of white-bordered black or iridescent blue feathers called a speculum on their wings; males especially tend to have blue speculum feathers. The mallard is long, of which the body makes up around two-thirds the length. The wingspan is and the bill is long. It is often slightly heavier than most other dabbling ducks, weighing . Mallards live in wetlands, eat water plants and small animals, and are social animals preferring to congregate in groups or flocks of varyin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Morphology (biology)
Morphology is a branch of biology dealing with the study of the form and structure of organisms and their specific structural features. This includes aspects of the outward appearance ( shape, structure, colour, pattern, size), i.e. external morphology (or eidonomy), as well as the form and structure of the internal parts like bones and organs, i.e. internal morphology (or anatomy). This is in contrast to physiology, which deals primarily with function. Morphology is a branch of life science dealing with the study of gross structure of an organism or taxon and its component parts. History The etymology of the word "morphology" is from the Ancient Greek (), meaning "form", and (), meaning "word, study, research". While the concept of form in biology, opposed to function, dates back to Aristotle (see Aristotle's biology), the field of morphology was developed by Johann Wolfgang von Goethe (1790) and independently by the German anatomist and physiologist Karl Friedr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fitness (biology)
Fitness (often denoted w or ω in population genetics models) is the 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 Darw ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Genotypes
The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a specific gene depends on the number of copies of each chromosome found in that species, also referred to as ploidy. In diploid species like humans, two full sets of chromosomes are present, meaning each individual has two alleles for any given gene. If both alleles are the same, the genotype is referred to as homozygous. If the alleles are different, the genotype is referred to as heterozygous. Genotype contributes to phenotype, the observable traits and characteristics in an individual or organism. The degree to which genotype affects phenotype depends on the trait. For example, the petal color in a pea plant is exclusively determined by genotype. The petals can be purple or white depending on the alleles present in the pea plant. H ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Introgression
Introgression, also known as introgressive hybridization, in genetics is the transfer of genetic material from one species into the gene pool of another by the repeated backcrossing of an interspecific hybrid with one of its parent species. Introgression is a long-term process, even when artificial; it may take many hybrid generations before significant backcrossing occurs. This process is distinct from most forms of gene flow in that it occurs between two populations of different species, rather than two populations of the same species. Introgression also differs from simple hybridization. Simple hybridization results in a relatively even mixture; gene and allele frequencies in the first generation will be a uniform mix of two parental species, such as that observed in mules. Introgression, on the other hand, results in a complex, highly variable mixture of genes, and may only involve a minimal percentage of the donor genome. Definition Introgression or introgressive hybridi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hybrid (biology)
In biology, a hybrid is the offspring resulting from combining the qualities of two organisms of different breeds, varieties, species or genera through sexual reproduction. Hybrids are not always intermediates between their parents (such as in blending inheritance), but can show hybrid vigor, sometimes growing larger or taller than either parent. The concept of a hybrid is interpreted differently in animal and plant breeding, where there is interest in the individual parentage. In genetics, attention is focused on the numbers of chromosomes. In taxonomy, a key question is how closely related the parent species are. Species are reproductively isolated by strong barriers to hybridisation, which include genetic and morphological differences, differing times of fertility, mating behaviors and cues, and physiological rejection of sperm cells or the developing embryo. Some act before fertilization and others after it. Similar barriers exist in plants, with differences in flowering t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Endogamy
Endogamy is the practice of marrying within a specific social group, religious denomination, caste, or ethnic group, rejecting those from others as unsuitable for marriage or other close personal relationships. Endogamy is common in many cultures and ethnic groups. Several religious and ethnic religious groups are traditionally more endogamous, although sometimes with the added dimension of requiring marital religious conversion. This permits an exogamous marriage, as the convert, by accepting the partner's religion, becomes accepted within the endogamous rules. Endogamy, as distinct from consanguinity, may result in transmission of genetic disorders, the so-called founder effect, within the relatively closed community. Adherence Endogamy can serve as a form of self-segregation; a community can use it to resist integrating and completely merging with surrounding populations. Minorities can use it to stay ethnically homogeneous over a long time as distinct communities within ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Outbreeding
Out-crossing or out-breeding is the technique of crossing between different breeds. This is the practice of introducing distantly related genetic material into a breeding line, thereby increasing genetic diversity. Outcrossing can be a useful technique in animal breeding. The outcrossing breeder intends to remove the traits by using "new blood." With dominant traits, one can still see the expression of the traits and can remove those traits whether one outcrosses, line breeds or inbreeds. With recessive traits, outcrossing allows for the recessive traits to migrate across a population. Many traits are Mendelian and therefore exhibit a more complicated intermediate phenotype. The outcrossing breeder then may have individuals that have many deleterious genes that may be expressed by subsequent inbreeding. There is now a gamut of deleterious genes within each individual in many dog breeds. Increasing the variation of genes or alleles within the gene pool may protect against extin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Assortative Mating
Assortative mating (also referred to as positive assortative mating or homogamy) is a mating pattern and a form of sexual selection in which individuals with similar phenotypes or genotypes mate with one another more frequently than would be expected under a random mating pattern. A majority of the phenotypes that are subject to assortative mating are body size, visual signals (e.g. color, pattern), and sexually selected traits such as crest size. The opposite of assortative is disassortative mating. Causes Several hypotheses have been proposed to explain the phenomenon of assortative mating. Assortative mating has evolved from a combination of different factors, which vary across different species. Assortative mating with respect to body size can arise as a consequence of intrasexual competition. In some species, size is correlated with fecundity in females. Therefore, males choose to mate with larger females, with the larger males defeating the smaller males in courting th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Genetic Pollution
Genetic pollution is a controversial term for uncontrolled gene flow into wild populations. It is defined as "the dispersal of contaminated altered genes from genetically engineered organisms to natural organisms, esp. by cross-pollination", but has come to be used in some broader ways. It is related to the population genetics concept of gene flow, and genetic rescue, which is genetic material intentionally introduced to increase the fitness of a population. It is called genetic pollution when it negatively impacts the fitness of a population, such as through outbreeding depression and the introduction of unwanted phenotypes which can lead to extinction. Conservation biologists and conservationists have used the term to describe gene flow from domestic, feral, and non-native species into wild indigenous species, which they consider undesirable. They promote awareness of the effects of introduced invasive species that may "''hybridize with native species, causing genetic poll ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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