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Mendel's laws
Mendel's laws (ˈmɛndəlz) pl n (Genetics) the principles of heredity proposed by Gregor Mendel. The Law of Segregation states that each hereditary character is determined by a pair of units in the reproductive cells: the pairs separate during meiosis so that each gamete carries only one unit of each pair. The Law of Independent Assortment states that the separation of the units of each pair is not influenced by that of any other pairMendel's Laws
Mendel's laws[′men·dəlz ‚lȯz] (genetics) Two basic principles of genetics formulated by Mendel: the law of segregation of alleles of a unit factor (gene), and the law of independent assortment of alleles of different unit factors. Mendel’s Laws principles describing the discrete, corpuscular nature of inheritance, discovered by G. Mendel. Mendel himself formulated only the law of combination of differentiating characters, which explained his discovery of the phenomena of segregation and the independent assortment of hereditary factors (later called genes) in the offspring of a cross. Three laws were usually accepted during the early phase of Mendelism—dominance, segregation, and independent assort-ment—thought to apply equally to the organism’s characters and to the hereditary factors in its germ cells. Therefore, the first law was thought to be that of dominance, according to which, in the first generation produced by crossing individuals differing in analogous (allelic) characters, only one (the dominant) is manifested, while the second, or alternative, remains hidden (recessive). A violation of the law of dominance was soon found with the intermediate manifestation of both characters in a first-generation hybrid. As a result, the name of Mendel’s first law was changed to that of the uniformity of first-generation hybrids. Mendel’s second law, usually called the law of segregation, becomes operative when first-generation hybrids are crossed or self-pollinated. The pairs of allelic genes are segregated, so that both dominant characters and the recessive characters that were latent in the preceding generation appear in the offspring in definite numerical ratios. Mendel’s third law, that of the independent assortment of characters, applies to crosses in which more than one pair of allelic genes combine: all pairs of participating alleles combine freely in the offspring, so that all possible combinations can occur—again, in definite numerical ratios. The third law is a direct consequence of segregation; it is more correct, therefore, to call it the law of the independent segregation of different pairs of alleles. Mendel demonstrated and calculated all possible types of segregation and combination of different pairs of genes, and he derived a general formula for the ratios he observed in the crosses. However, this formula is valid only for the combination of the genes themselves. As for the characters actually manifested in development, subsequent research disclosed a number of complications caused by the patterns of interaction of the various genes during the development of the characters they determine (pleiotropy, polygenism, epistasis). These interactions should therefore not be regarded as contradicting the law of independent segregation or combination, which is in fact partly violated only in regard to the phenomena of gene linkage (discovered subsequently). A careful distinction must be made between the principles related to the transmission and distribution of hereditary factors in the offspring and those principles related to the realization of these factors in the development of the organism. The former, which are genotypic, include Mendel’s laws of segregation and independent assortment, the latter, which are phenotypic, are concerned with dominance, intermediate manifestation, and many other forms of allelic and nonallelic interactions. Mendel’s laws have been completely confirmed and explained by the chromosome theory. A. E. GAISINOVICH Mendel's laws
Mendel's laws [men´delz] in the inheritance of certain traits or characters, offspring are not intermediate in type between the parents, but inherit from one or the other parent in this respect. Thus, if a plant with the factor tallness (TT) is mated with one with the factor shortness (SS), then the offspring will inherit these factors in the ratio TT, 2Ts, SS. This law is usually expressed as the law of independent assortment and the law of segregation.law (lo) 1. A scientific statement that is found to apply to a class of natural occurrences.2. A body of rules, regulations, and legal opinions of conduct and action that are made by controlling authority and are legally binding.administrative lawBody of law in the form of decisions, rules, regulations, and orders created by administrative agencies under the direction of the executive branch of the government used to carry out the duties of such agencies. Regulations of nursing practice, for example, are considered administrative laws. all-or-none lawThe weakest stimulus capable of producing a response produces the maximum contraction of cardiac and skeletal muscle cells, and the maximal impulse transmission rate in neurons.apology lawA colloquial term for any legal statute that encourages health care providers to acknowledge and disclose medical errors openly. Although apology laws vary from one jurisdiction to another, most include some measure of legal protection for the individual or agency making the apology. Avogadro's law See: Avogadro, AmedeoBaruch's law See: Baruch's lawBeer's law See: Beer's lawBell's law See: Bell, Sir Charleslaw of Bergonié and TribondeauA fundamental law of radiation biology that states that the radiosensitivity of a tissue is increased the greater the number of undifferentiated cells in the tissue, the greater the mitotic activity, and the greater the length of time that they are actively proliferating.biogenetic lawOntogeny recapitulates phylogeny, i.e., an individual in its development recapitulates stages in its evolutionary development. Synonym: Haeckel's lBoyle's law See: Boyle's lawcase lawOpinions or decisions made by the courts.Charles' law See: Charles' lawcommon lawA system of law that originated in medieval England and is based on former legal decisions (precedent) and custom, not on legislation. Common law constantly evolves from previous decisions and changing custom. It forms the basis of the legal system in the U.S. (except Louisiana), the U.K. and most other English-speaking countries and is therefore the most frequent source of legal precedent for malpractice cases. cosine law1. A physical law that describes the relationship between the sides and angles of any triangle.2. When applied to physical treatment of the body, it describes the effectiveness of radiant energy and the angle at which it strikes tissue. The maximum amount of energy transfer occurs when the energy strikes tissue at a 90° angle. As the angle changes, the effectiveness of the energy is reduced by the multiple of the cosine of the angle: Effective energy = applied energy × cosine of the angle. law of contiguity1. A law stating that if two ideas occur together, then the recollection of one will likely stimulate recall of the other.2. A law stating that if combined stimuli precede contraction of a muscle, then, when those stimuli are repeated, the muscle will contract again.Courvoisier's law See: Courvoisier's lawcriminal lawThe area of the law relating to violations of statutes that pertain to public offenses or acts committed against the public. For example, a health care provider can be prosecuted for criminal acts such as assault and battery, fraud, and abuse. Dalton's law See: Dalton's lawlaw of definite proportionsTwo or more elements when united to form a new substance do so in a constant and fixed proportion by weight. See: Dalton's lawlaw of effectThe psychological principle that positively reinforced behaviors will be repeated and negatively reinforced behaviors will diminish or be extinguished.Fechner's law See: Fechner's lawFick's law See: Fick, Adolf EugenFrank-Starling law See: Starling's law.fraud and abuse lawA statute that regulates the appropriateness of health care provider behavior in billing practices, receipt of payments, and provision of medically necessary services.Gay-Lussac's lawCharles' law.Good Samaritan lawThe legal protection given to those who stop and render care in an emergency situation without expectation for remuneration. The necessity for this legislation arose when physicians who assisted in giving emergency care were later accused of malpractice by the patient. Graham's law See: Graham's lawlaw of Grotthus-Draper See: Grotthus-Draper, law ofGudden's law See: Gudden, Bernhard Alloys vonHaeckel's lawBiogenetic law.law of the heartOther things being equal, the stroke volume of the heart varies as the extent of diastolic filling, that is, the energy of contraction is a function of the initial length of the muscle fibers.Hellin's law See: Hellin's lawHenry's law See: Henry's lawHilton's law See: Hilton, JohnHooke's law See: Hooke's lawlaw of the intestineModerate distention of the intestine at a point causes relaxation below (aborally to the point) and contraction above.inverse-square lawThe intensity of radiation or light at any distance is inversely proportional to the square of the distance between the irradiated surface and a point source. Thus, a light with a certain intensity at a 4-ft distance will have only one-fourth that intensity at 8 ft and would be four times as intense at a 2-ft distance. law of Laplace See: law of Laplacelaw of MagendieBell's law.Marey's law See: Marey's lawMariotte's lawBoyle's law.law of mass actionIn any chemical reaction, the ratio of the mathematical products of the concentrations of the products (raised to the power of the chemical coefficients in the balanced equation) to the mathematical products of the concentrations of the reactants (similarly raised) is constant at a given temperature.Mendel's laws See: Mendel's lawslaw of multiple proportionsWhen two substances unite to form a series of chemical compounds, the proportions in which they unite are simple multiples of one another or of one common proportion. See: Dalton's lawNysten's law See: Nysten's lawOhm's law See: Ohm's lawperiodic lawThe physical and chemical properties of chemical elements are periodic functions of their atomic number. A natural classification of elements is made according to their atomic number. When arranged in order (through calcium, atomic number 20), elements show regular variations in most of their physical and chemical properties. Poiseuille's law See: Poiseuille's lawQ lawAs temperature (in degrees Kelvin) decreases, chemical activity decreases.law of reciprocal proportionsIn chemistry, the proportions in which two elementary bodies unite with a third one are simple multiples or simple fractions of the proportions in which these two bodies unite with each other.reciprocity lawAny milliamperage multiplied by an exposure time setting that gives the same milliamperage-second outcome should give the same relative density to an image. However, this law is dramatically affected by the image receptor response curve, esp. when it is not a 45° linear curve. In radiographic intensifying film and screen technologies, the reciprocity law does not hold at long exposure times because of the reversal of the D log E response curve. right-to-know lawA law that dictates that employers must inform their employees of the health effects and chemical hazards of the toxic substances used in each workplace. The employer must provide information concerning the generic and chemical names of the substances used; the level at which the exposure is hazardous; the effects of exposure at hazardous levels; the symptoms of such effects; the potential for flammability, explosion, and reactivity of the substances; the appropriate emergency treatment; proper conditions for safe use and exposure to the substances; and procedures for cleanup of leaks and spills. The law provides that an employee may refuse to work with a toxic substance until he or she has received information concerning its potential for hazard. See: hazardous material; health hazard; material safety data sheet; permissible exposure limitsRubner's laws See: Rubner's lawsStarling's law See: Starling's lawStarling's law of intestine See: Starling's law of intestineStoke's law See: Stoke's lawSutton's law See: Sutton's lawvan 't Hoff's law See: van 't Hoff's lawWaller's law of degeneration See: Waller's law of degenerationWeber's law See: Weber's lawWeigert law See: Weigert, CarlWolff's law See: Wolff's lawMendel's laws see MENDELIAN GENETICS.LegalSeelaw |