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Molecular Drive
Molecular drive is a term coined by Gabriel Dover in 1982 to describe evolutionary processes that change the genetic composition of a population through DNA turnover mechanisms. Molecular drive operates independently of natural selection and genetic drift. The best-known such process is the concerted evolution of genes present in many tandem copies, such as those for ribosomal RNAs or silk moth egg shell chorion proteins, in sexually reproducing species. The concept has been proposed to extend to the diversification of multigene families. The mechanisms involved include gene conversion, unequal crossing-over, transposition, slippage replication and RNA-mediated exchanges. Because mutations changing the sequence of one copy are less common than deletions, duplications and replacement of one copy by another, the copies gradually come to resemble each other much more than they would if they had been evolving independently. Concerted evolution can be unbiased, in which case eve ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Adaptation
In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the population during that process. Thirdly, it is a phenotypic trait or adaptive trait, with a functional role in each individual organism, that is maintained and has evolved through natural selection. Historically, adaptation has been described from the time of the ancient Greek philosophers such as Empedocles and Aristotle. In 18th and 19th century natural theology, adaptation was taken as evidence for the existence of a deity. Charles Darwin proposed instead that it was explained by natural selection. Adaptation is related to biological fitness, which governs the rate of evolution as measured by change in allele frequencies. Often, two or more species co-adapt and co-evolve as they develop adaptations that interlock with those of the oth ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Unequal Crossing-over
Unequal crossing over is a type of gene duplication or deletion event that deletes a sequence in one strand and replaces it with a duplication from its sister chromatid in mitosis or from its homologous chromosome during meiosis. It is a type of chromosomal crossover between homologous sequences that are not paired precisely. Normally genes are responsible for occurrence of crossing over. It exchanges sequences of different links between chromosomes. Along with gene conversion, it is believed to be the main driver for the generation of gene duplications and is a source of mutation in the genome. Mechanisms During meiosis, the duplicated chromosomes (chromatids) in eukaryotic organisms are attached to each other in the centromere region and are thus paired. The maternal and paternal chromosomes then align alongside each other. During this time, recombination can take place via crossing over of sections of the paternal and maternal chromatids and leads to reciprocal recombinat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Evolutionary Biology
Evolutionary biology is the subfield of biology that studies the evolutionary processes (natural selection, common descent, speciation) that produced the diversity of life on Earth. It is also defined as the study of the history of life forms on Earth. Evolution is based on the theory that all species are related and they gradually change over time. In a population, the genetic variations affect the physical characteristics i.e. phenotypes of an organism. These changes in the phenotypes will be an advantage to some organisms, which will then be passed onto their offspring. Some examples of evolution in species over many generations are the Peppered Moth and Flightless birds. In the 1930s, the discipline of evolutionary biology emerged through what Julian Huxley called the modern synthesis of understanding, from previously unrelated fields of biological research, such as genetics and ecology, systematics, and paleontology. The importance of studying Evolutionary biology is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Promoter (biology)
In genetics, a promoter is a sequence of DNA to which proteins bind to initiate transcription of a single RNA transcript from the DNA downstream of the promoter. The RNA transcript may encode a protein (mRNA), or can have a function in and of itself, such as tRNA or rRNA. Promoters are located near the transcription start sites of genes, upstream on the DNA (towards the 5' region of the sense strand). Promoters can be about 100–1000 base pairs long, the sequence of which is highly dependent on the gene and product of transcription, type or class of RNA polymerase recruited to the site, and species of organism. Promoters control gene expression in bacteria and eukaryotes. RNA polymerase must attach to DNA near a gene for transcription to occur. Promoter DNA sequences provide an enzyme binding site. The -10 sequence is TATAAT. -35 sequences are conserved on average, but not in most promoters. Artificial promoters with conserved -10 and -35 elements transcribe more slowly. All D ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Non-mendelian Inheritance
Non-Mendelian inheritance is any pattern in which traits do not segregate in accordance with Mendel's laws. These laws describe the inheritance of traits linked to single genes on chromosomes in the nucleus. In Mendelian inheritance, each parent contributes one of two possible alleles for a trait. If the genotypes of both parents in a genetic cross are known, Mendel's laws can be used to determine the distribution of phenotypes expected for the population of offspring. There are several situations in which the proportions of phenotypes observed in the progeny do not match the predicted values. Non-Mendelian inheritance plays a role in several disease which affected the processes. Types Incomplete dominance In cases of intermediate inheritance due to incomplete dominance, the principle of dominance discovered by Mendel does not apply. Nevertheless, the principle of uniformity works, as all offspring in the F1-generation have the same genotype and same phenotype. Mendel's prin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transformation (genetics)
In molecular biology and genetics, transformation is the genetic alteration of a cell resulting from the direct uptake and incorporation of exogenous genetic material from its surroundings through the cell membrane(s). For transformation to take place, the recipient bacterium must be in a state of competence, which might occur in nature as a time-limited response to environmental conditions such as starvation and cell density, and may also be induced in a laboratory. Transformation is one of three processes that lead to horizontal gene transfer, in which exogenous genetic material passes from one bacterium to another, the other two being conjugation (transfer of genetic material between two bacterial cells in direct contact) and transduction (injection of foreign DNA by a bacteriophage virus into the host bacterium). In transformation, the genetic material passes through the intervening medium, and uptake is completely dependent on the recipient bacterium. As of 2014 about 8 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among the first life forms to appear on Earth, and are present in most of its habitats. Bacteria inhabit soil, water, acidic hot springs, radioactive waste, and the deep biosphere of Earth's crust. Bacteria are vital in many stages of the nutrient cycle by recycling nutrients such as the fixation of nitrogen from the atmosphere. The nutrient cycle includes the decomposition of dead bodies; bacteria are responsible for the putrefaction stage in this process. In the biological communities surrounding hydrothermal vents and cold seeps, extremophile bacteria provide the nutrients needed to sustain life by converting dissolved compounds, such as hydrogen sulphide and methane, to energy. Bacteria also live in symbiotic and parasitic relationsh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Meiotic Drive
Meiotic drive is a type of intragenomic conflict, whereby one or more loci within a genome will effect a manipulation of the meiotic process in such a way as to favor the transmission of one or more alleles over another, regardless of its phenotypic expression. More simply, meiotic drive is when one copy of a gene is passed on to offspring more than the expected 50% of the time. According to Buckler et al., "Meiotic drive is the subversion of meiosis so that particular genes are preferentially transmitted to the progeny. Meiotic drive generally causes the preferential segregation of small regions of the genome". Meiotic drive in plants The first report of meiotic drive came from Marcus Rhoades who in 1942 observed a violation of mendelian segregation ratios for the R locus - a gene controlling the production of the purple pigment anthocyanin in maize kernels - in a maize line carrying abnormal chromosome 10. This violation of mendelian segregation was later shown to be the result ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gene Duplication
Gene duplication (or chromosomal duplication or gene amplification) is a major mechanism through which new genetic material is generated during molecular evolution. It can be defined as any duplication of a region of DNA that contains a gene. Gene duplications can arise as products of several types of errors in DNA replication and repair machinery as well as through fortuitous capture by selfish genetic elements. Common sources of gene duplications include ectopic recombination, retrotransposition event, aneuploidy, polyploidy, and replication slippage. Mechanisms of duplication Ectopic recombination Duplications arise from an event termed unequal crossing-over that occurs during meiosis between misaligned homologous chromosomes. The chance of it happening is a function of the degree of sharing of repetitive elements between two chromosomes. The products of this recombination are a duplication at the site of the exchange and a reciprocal deletion. Ectopic recombination is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Deletion (genetics)
In genetics, a deletion (also called gene deletion, deficiency, or deletion mutation) (sign: Δ) is a mutation (a genetic aberration) in which a part of a chromosome or a sequence of DNA is left out during DNA replication. Any number of nucleotides can be deleted, from a single base to an entire piece of chromosome. Some chromosomes have fragile spots where breaks occur which result in the deletion of a part of chromosome. The breaks can be induced by heat, viruses, radiations, chemicals. When a chromosome breaks, a part of it is deleted or lost, the missing piece of chromosome is referred to as deletion or a deficiency. For synapsis to occur between a chromosome with a large intercalary deficiency and a normal complete homolog, the unpaired region of the normal homolog must loop out of the linear structure into a deletion or compensation loop. The smallest single base deletion mutations occur by a single base flipping in the template DNA, followed by template DNA strand sli ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mutation
In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, mitosis, or meiosis or other types of damage to DNA (such as pyrimidine dimers caused by exposure to ultraviolet radiation), which then may undergo error-prone repair (especially microhomology-mediated end joining), cause an error during other forms of repair, or cause an error during replication (translesion synthesis). Mutations may also result from insertion or deletion of segments of DNA due to mobile genetic elements. Mutations may or may not produce detectable changes in the observable characteristics (phenotype) of an organism. Mutations play a part in both normal and abnormal biological processes including: evolution, cancer, and the development of the immune system, including junctional diversity. Mutation is the ultimate source o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Slipped Strand Mispairing
Slipped strand mispairing (SSM), (also known as replication slippage), is a mutation process which occurs during DNA replication. It involves denaturation and displacement of the DNA strands, resulting in mispairing of the complementary bases. Slipped strand mispairing is one explanation for the origin and evolution of repetitive DNA sequences. It is a form of mutation that leads to either a trinucleotide or dinucleotide expansion, or sometimes contraction, during DNA replication.Hartl L.D and Ruvolo M, 2012, Genetic Analysis of Genes and Genomes, Jones & Bartlett Learning, Burlington, pg. 529 A slippage event normally occurs when a sequence of repetitive nucleotides (tandem repeats) are found at the site of replication. Tandem repeats are unstable regions of the genome where frequent insertions and deletions of nucleotides can take place, resulting in genome rearrangements. DNA polymerase, the main enzyme to catalyze the polymerization of free deoxyribonucleotides into a newl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
