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Microevolution
Microevolution is the change in allele frequencies that occurs over time within a population. This change is due to four different processes: mutation, selection (natural and artificial), gene flow and genetic drift. This change happens over a relatively short (in evolutionary terms) amount of time compared to the changes termed macroevolution. Population genetics is the branch of biology that provides the mathematical structure for the study of the process of microevolution. Ecological genetics concerns itself with observing microevolution in the wild. Typically, observable instances of evolution are examples of microevolution; for example, bacterial strains that have antibiotic resistance. Microevolution may lead to speciation, which provides the raw material for macroevolution. Difference from macroevolution Macroevolution is guided by sorting of interspecific variation ("species selection"), as opposed to sorting of intraspecific variation in microevolution. Species selecti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Macroevolution
Macroevolution usually means the evolution of large-scale structures and traits that go significantly beyond the intraspecific variation found in microevolution (including speciation). In other words, macroevolution is the evolution of taxa above the species level (genera, families, orders, etc.). Macroevolution is often thought to require the evolution of completely new structures such as entirely new organs. However, fundamentally novel structures are not necessary for dramatic evolutionary change. For instance, the evolution of mammal diversity in the past 100 million years has not required any major innovation. All of this diversity can be explained by modification of existing organs. In most cases, macroevolution cannot be observed directly because numerous mutations are required for large-scale changes. Hence specific methods are required to study and prove it. However, in rare cases single mutations can cause dramatic change and thus serve as models for macro-evolutionary ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Macroevolution
Macroevolution usually means the evolution of large-scale structures and traits that go significantly beyond the intraspecific variation found in microevolution (including speciation). In other words, macroevolution is the evolution of taxa above the species level (genera, families, orders, etc.). Macroevolution is often thought to require the evolution of completely new structures such as entirely new organs. However, fundamentally novel structures are not necessary for dramatic evolutionary change. For instance, the evolution of mammal diversity in the past 100 million years has not required any major innovation. All of this diversity can be explained by modification of existing organs. In most cases, macroevolution cannot be observed directly because numerous mutations are required for large-scale changes. Hence specific methods are required to study and prove it. However, in rare cases single mutations can cause dramatic change and thus serve as models for macro-evolutionary ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Evolution
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation tends to exist within any given population as a result of genetic mutation and recombination. Evolution occurs when evolutionary processes such as natural selection (including sexual selection) and genetic drift act on this variation, resulting in certain characteristics becoming more common or more rare within a population. The evolutionary pressures that determine whether a characteristic is common or rare within a population constantly change, resulting in a change in heritable characteristics arising over successive generations. It is this process of evolution that has given rise to biodiversity at every level of biological organisation, including the levels of species, individual organisms, and molecules. The theory of evolution by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Antibiotic Resistance
Antimicrobial resistance (AMR) occurs when microbes evolve mechanisms that protect them from the effects of antimicrobials. All classes of microbes can evolve resistance. Fungi evolve antifungal resistance. Viruses evolve antiviral resistance. Protozoa evolve antiprotozoal resistance, and bacteria evolve antibiotic resistance. Those bacteria that are considered extensively drug resistant (XDR) or totally drug-resistant (TDR) are sometimes called "superbugs".A.-P. Magiorakos, A. Srinivasan, R. B. Carey, Y. Carmeli, M. E. Falagas, C. G. Giske, S. Harbarth, J. F. Hinndler ''et al''Multidrug-resistant, extensively drug-resistant and pandrug-resistant bacteria... Clinical Microbiology and Infection, Vol 8, Iss. 3 first published 27 July 2011 ia Wiley Online Library Retrieved 28 August 2020 Although antimicrobial resistance is a naturally-occurring process, it is often the result of improper usage of the drugs and management of the infections. Antibiotic resistance is a major subset ... [...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] |
Population Genetics
Population genetics is a subfield of genetics that deals with genetic differences within and between populations, and is a part of evolutionary biology. Studies in this branch of biology examine such phenomena as adaptation, speciation, and population structure. Population genetics was a vital ingredient in the emergence of the modern evolutionary synthesis. Its primary founders were Sewall Wright, J. B. S. Haldane and Ronald Fisher, who also laid the foundations for the related discipline of quantitative genetics. Traditionally a highly mathematical discipline, modern population genetics encompasses theoretical, laboratory, and field work. Population genetic models are used both for statistical inference from DNA sequence data and for proof/disproof of concept. What sets population genetics apart from newer, more phenotypic approaches to modelling evolution, such as evolutionary game theory and adaptive dynamics, is its emphasis on such genetic phenomena as dominance, epi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
DNA Replication
In molecular biology, DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. DNA replication occurs in all living organisms acting as the most essential part for biological inheritance. This is essential for cell division during growth and repair of damaged tissues, while it also ensures that each of the new cells receives its own copy of the DNA. The cell possesses the distinctive property of division, which makes replication of DNA essential. DNA is made up of a double helix of two complementary strands. The double helix describes the appearance of a double-stranded DNA which is thus composed of two linear strands that run opposite to each other and twist together to form. During replication, these strands are separated. Each strand of the original DNA molecule then serves as a template for the production of its counterpart, a process referred to as semiconservative replication. As a result of semi-conservative rep ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cellular Processes
The cell is the basic structural and functional unit of life forms. Every cell consists of a cytoplasm enclosed within a membrane, and contains many biomolecules such as proteins, DNA and RNA, as well as many small molecules of nutrients and metabolites.Cell Movements and the Shaping of the Vertebrate Body in Chapter 21 of Molecular Biology of the Cell '' fourth edition, edited by Bruce Alberts (2002) published by Garland Science. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos. It is also common to describe small molecules such as < ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Somatic Hypermutation
Somatic hypermutation (or SHM) is a cellular mechanism by which the immune system adapts to the new foreign elements that confront it (e.g. microbes), as seen during class switching. A major component of the process of affinity maturation, SHM diversifies B cell receptors used to recognize foreign elements (antigens) and allows the immune system to adapt its response to new threats during the lifetime of an organism. Somatic hypermutation involves a programmed process of mutation affecting the variable regions of immunoglobulin genes. Unlike germline mutation, SHM affects only an organism's individual immune cells, and the mutations are not transmitted to the organism's offspring.Oprea, M. (1999''Antibody Repertoires and Pathogen Recognition:'' The Role of Germline Diversity and Somatic Hypermutation'' (Thesis) University of Leeds.'' Because this mechanism is merely selective and not precisely targeted, somatic hypermutation has been strongly implicated in the development of B-cell l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Proofreading (biology)
The term proofreading is used in genetics to refer to the error-correcting processes, first proposed by John Hopfield and Jacques Ninio, involved in DNA replication, immune system specificity, enzyme-substrate recognition among many other processes that require enhanced specificity. The proofreading mechanisms of Hopfield and Ninio are non-equilibrium active processes that consume ATP to enhance specificity of various biochemical reactions. In bacteria, all three DNA polymerases (I, II and III) have the ability to proofread, using 3’ → 5’ exonuclease activity. When an incorrect base pair is recognized, DNA polymerase reverses its direction by one base pair of DNA and excises the mismatched base. Following base excision, the polymerase can re-insert the correct base and replication can continue. In eukaryotes, only the polymerases that deal with the elongation (delta and epsilon) have proofreading ability (3’ → 5’ exonuclease activity). Proofreading also occurs in mRNA ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Allele Frequencies
Allele frequency, or gene frequency, is the relative frequency of an allele (variant of a gene) at a particular locus in a population, expressed as a fraction or percentage. Specifically, it is the fraction of all chromosomes in the population that carry that allele over the total population or sample size. Microevolution is the change in allele frequencies that occurs over time within a population. Given the following: # A particular locus on a chromosome and a given allele at that locus # A population of ''N'' individuals with ploidy ''n'', i.e. an individual carries ''n'' copies of each chromosome in their somatic cells (e.g. two chromosomes in the cells of diploid species) # The allele exists in ''i'' chromosomes in the population then the allele frequency is the fraction of all the occurrences ''i'' of that allele and the total number of chromosome copies across the population, ''i''/(''nN''). The allele frequency is distinct from the genotype frequency, although they are re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
DNA Polymerase
A DNA polymerase is a member of a family of enzymes that catalyze the synthesis of DNA molecules from nucleoside triphosphates, the molecular precursors of DNA. These enzymes are essential for DNA replication and usually work in groups to create two identical DNA duplexes from a single original DNA duplex. During this process, DNA polymerase "reads" the existing DNA strands to create two new strands that match the existing ones. These enzymes catalyze the chemical reaction : deoxynucleoside triphosphate + DNAn pyrophosphate + DNAn+1. DNA polymerase adds nucleotides to the three prime (3')-end of a DNA strand, one nucleotide at a time. Every time a cell divides, DNA polymerases are required to duplicate the cell's DNA, so that a copy of the original DNA molecule can be passed to each daughter cell. In this way, genetic information is passed down from generation to generation. Before replication can take place, an enzyme called helicase unwinds the DNA molecule from its tightl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
