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Intragenomic Conflict
Intragenomic conflict refers to the evolutionary phenomenon where genes have phenotypic effects that promote their own transmission in detriment of the transmission of other genes that reside in the same genome. The selfish gene theory postulates that natural selection will increase the frequency of those genes whose phenotypic effects cause their transmission to new organisms, and most genes achieve this by cooperating with other genes in the same genome to build an organism capable of reproducing and/or helping kin to reproduce. The assumption of the prevalence of intragenomic cooperation underlies the organism-centered concept of inclusive fitness. However, conflict among genes in the same genome may arise both in events related to reproduction (a selfish gene may "cheat" and increase its own presence in gametes or offspring above the expected according to fair Mendelian segregation and fair gametogenesis) and altruism (genes in the same genome may disagree on how to value ot ... [...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] |
Allele
An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the 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 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 grouping is controlled by the 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 in little or no change in the function of the gene product it codes for. However, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Centromere
The centromere links a pair of sister chromatids together during cell division. This constricted region of chromosome connects the sister chromatids, creating a short arm (p) and a long arm (q) on the chromatids. During mitosis, spindle fibers attach to the centromere via the kinetochore. The physical role of the centromere is to act as the site of assembly of the kinetochores – a highly complex multiprotein structure that is responsible for the actual events of chromosome segregation – i.e. binding microtubules and signaling to the cell cycle machinery when all chromosomes have adopted correct attachments to the spindle, so that it is safe for cell division to proceed to completion and for cells to enter anaphase. There are, broadly speaking, two types of centromeres. "Point centromeres" bind to specific proteins that recognize particular DNA sequences with high efficiency. Any piece of DNA with the point centromere DNA sequence on it will typically form a centromere if pr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Neocentromere
Neocentromeres are new centromeres that form at a place on the chromosome that is usually not centromeric. They typically arise due to disruption of the normal centromere. These neocentromeres should not be confused with “knobs”, which were also described as “neocentromeres” in maize in the 1950s. Unlike most normal centromeres, neocentromeres do not contain satellite sequences that are highly repetitive but instead consist of unique sequences. Despite this, most neocentromeres are still able to carry out the functions of normal centromeres in regulating chromosome segregation and inheritance. This raises many questions on what is necessary versus what is sufficient for constituting a centromere. As neocentromeres are still a relatively new phenomenon in cell biology and genetics, it may be useful to keep in mind that neocentromeres may be somewhat related to point centromeres, holocentromeres, and regional centromeres. Whereas point centromeres are defined by sequence, re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polar Bodies
A polar body is a small haploid cell that is formed at the same time as an egg cell during oogenesis, but generally does not have the ability to be fertilized. It is named from its polar position in the egg. When certain diploid cells in animals undergo cytokinesis after meiosis to produce egg cells, they sometimes divide unevenly. Most of the cytoplasm is segregated into one daughter cell, which becomes the egg or ovum, while the smaller ''polar bodies'' only get a small amount of cytoplasm. They frequently die and disintegrate by apoptosis, but in some cases remain and can be important in the life cycle of the organism. Twinning ''Polar body twinning'' is a hypothesized form of twinning in meiosis, where one or more polar bodies do not disintegrate and are fertilized by sperm. Twinning would occur, in principle, if the egg cell and a polar body were both fertilized by separate sperms. However, even if fertilization occurs, further development would usually not occur beca ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oocyte
An oocyte (, ), oöcyte, or ovocyte is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in a female fetus in the ovary during female gametogenesis. The female germ cells produce a primordial germ cell (PGC), which then undergoes mitosis, forming oogonia. During oogenesis, the oogonia become primary oocytes. An oocyte is a form of genetic material that can be collected for cryoconservation. Formation The formation of an oocyte is called oocytogenesis, which is a part of oogenesis. Oogenesis results in the formation of both primary oocytes during fetal period, and of secondary oocytes after it as part of ovulation. Characteristics Cytoplasm Oocytes are rich in cytoplasm, which contains yolk granules to nourish the cell early in development. Nucleus During the primary oocyte stage of oogenesis, the nucleus is called a germinal vesicle. The only normal human type of secondary oocyte has t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Meiosis
Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately result in four cells with only one copy of each chromosome ( haploid). Additionally, prior to the division, genetic material from the paternal and maternal copies of each chromosome is crossed over, creating new combinations of code on each chromosome. Later on, during fertilisation, the haploid cells produced by meiosis from a male and female will fuse to create a cell with two copies of each chromosome again, the zygote. Errors in meiosis resulting in aneuploidy (an abnormal number of chromosomes) are the leading known cause of miscarriage and the most frequent genetic cause of developmental disabilities. In meiosis, DNA replication is followed by two rounds of cell division to produce four daughter cells, each with half the number of chr ... [...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] |
Fungus
A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from the other eukaryotic kingdoms, which by one traditional classification include Plantae, Animalia, Protozoa, and Chromista. A characteristic that places fungi in a different kingdom from plants, bacteria, and some protists is chitin in their cell walls. Fungi, like animals, are heterotrophs; they acquire their food by absorbing dissolved molecules, typically by secreting digestive enzymes into their environment. Fungi do not photosynthesize. Growth is their means of mobility, except for spores (a few of which are flagellated), which may travel through the air or water. Fungi are the principal decomposers in ecological systems. These and other differences place fungi in a single group of related organisms, named the ''Eumycota'' (''true f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Neurospora
''Neurospora'' is a genus of Ascomycete fungi. The genus name, meaning "nerve spore" refers to the characteristic striations on the spores that resemble axons. The best known species in this genus is ''Neurospora crassa'', a common model organism in biology. ''Neurospora intermedia'' var. ''oncomensis'' is believed to be the only mold belonging to ''Neurospora'' which is used in food production (to make oncom). Characteristics ''Neurospora'' species are molds with broadly spreading colonies, with abundant production of ascomata. Ascomata are superficial or immersed, perithecial and ostiolate or cleistothecial and non-ostiolate, hairy or glabrous, dark coloured. Peridium membranaceous, asci cylindrical, clavate or subspherical, with a persistent or evanescent wall, usually with a thickened and non-amyloid annular structure at the apex, usually 8-spored. Ascospores broadly fusiform, ellipsoidal, or nearly spherical, unicellular, hyaline to yellowish brown or olive-brown, becomin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mouse
A mouse ( : mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus''). Mice are also popular as pets. In some places, certain kinds of field mice are locally common. They are known to invade homes for food and shelter. Mice are typically distinguished from rats by their size. Generally, when a muroid rodent is discovered, its common name includes the term ''mouse'' if it is smaller, or ''rat'' if it is larger. The common terms ''rat'' and ''mouse'' are not taxonomically specific. Typical mice are classified in the genus '' Mus'', but the term ''mouse'' is not confined to members of ''Mus'' and can also apply to species from other genera such as the deer mouse, ''Peromyscus''. Domestic mice sold as pets often differ substantially in size from the common house mouse. This is attributable to breeding a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mus Musculus
Mus or MUS may refer to: Abbreviations * MUS, the NATO country code for Mauritius * MUS, the IATA airport code for Minami Torishima Airport * MUS, abbreviation for the Centre for Modern Urban Studies on Campus The Hague, Leiden University, Netherlands * MUS, abbreviation for Medically unexplained physical symptoms * MUS, abbreviation for the Memphis University School * MUS, abbreviation for the Movimiento Unión Soberanista * MUS, abbreviation for Multiple-use water supply system, a low-cost, equitable water supply systems * Mus, abbreviation for Musca, a southern constellation * mus, ISO-639 code for the Muscogee language * Mus., abbreviation used in music degrees such as B.Mus. and M.Mus. * MUs, or million units of energy, used in India for a gigawatt hour People * Anders Mus (fl. 1501–1535), Danish civil servant in Norway * Conny Mus (1950–2010), Dutch journalist, best known as a correspondent for ''RTL Nieuws'' in Israel and the Middle East * Gus Mus (born 1944), I ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
