Hardy-Weinberg law

Har·dy-Wein·berg law

H0063950 (här′dē-wīn′bûrg)n. A fundamental principle in population genetics stating that the genotype frequencies and gene frequencies of a large, randomly mating population remain constant provided immigration, mutation, and selection do not take place.

[After Godfrey Harold Hardy (1877-1947), British mathematician, and Wilhelm , Weinberg (1862-1937), German physician.]

Hardy-Weinberg Law

Hardy-Weinberg law

[¦här·dē ′wīn‚bərg ‚lȯ] (genetics) The concept that frequencies of both genes and genotypes will remain constant from generation to generation in an idealized population where mating is random and evolutionary forces (such as mutation, migration, selection, or genetic drift) are absent.

Hardy-Weinberg Law

a law of population genetics that establishes the relationship between the frequencies of the genes and genotypes in a freely interbreeding population. The law was independently formulated in 1908 by the British mathematician G. Hardy and the German physician W. Weinberg.

According to this law, if the number of diploid organisms in a population is so large that one may ignore occasional fluctuations in gene frequencies (that is, genetic drift), and in the absence of mutation, migration, and selection (with respect to the gene in question), the frequencies of genotypes AA, Aa, and aa in a given population, after the first generation, will remain the same in the succeeding generations. According to the Hardy-Weinberg formula, the frequencies of genotypes AA, Aa, and aa will be equal to p², 2pq, and q², respectively, where A and a represent the alleles of a gene that is not sex-linked, p represents the frequency of allele A, and q represents the frequency of allele a. The Hardy-Weinberg law also applies to multiallelic genes.

In polyploid populations—as well as in the case of sex-linked genes in diploid populations—the relative proportions are only established over many generations. Even though a given population may conform to the Hardy-Weinberg formula, this is not necessarily proof that the population is unaffected by genetic processes. For example, the interbreeding of closely related individuals (that is, inbreeding), which increases the proportion of homozygotes in the population, when combined with selection against homozygotes may lead to genotype frequencies corresponding to the Hardy-Weinberg formula. By comparing the actually observed frequencies of genotypes to the frequencies theoretically expected according to the Hardy-Weinberg law, it is possible in a number of cases to gauge the frequencies of the alleles, to single out the factors influencing the alleles, and to obtain quantitative data pertaining, for example, to selection, non-random interbreeding, migration, and chance fluctuations.

The concept of the genetic equilibrium of populations, as first expressed in the Hardy-Weinberg law, underlies the modern view of the interacting processes of population genetics.

REFERENCES

Timofeev-Resovskii, N. V., A. V. Iablokov, and N. V. Glotov. Ocherk ucheniia opopuliatsii. Moscow, 1973.
Mettler, L., and T. Gregg. Genetika populiatsii i evoliutsiia. Moscow, 1972. (Translated from English.)
Li, C. C. First Course in Population Genetics. California, 1975.

L. A. ZHIVOTOVSKII

See

Hardy-Weinberg law

Har·dy-Wein·berg law

(har'dē wīn'bĕrg), if mating occurs at random with respect to any one autosomal locus in a population in which the gene frequencies are equal in the two sexes, and the factors tending to change gene frequencies (mutation, differential selection, migration) are either absent or negligible, then in one generation the probabilities of all possible genotypes will on average equal the same proportions as if the genes were assembled at random. The law does not apply to two or more loci jointly, nor to X-linked traits where the initial gene frequencies differ in the two sexes.

Hardy-Weinberg law

(här′dē-wīn′bûrg)n. A fundamental principle in population genetics stating that the genotype frequencies and gene frequencies of a large, randomly mating population remain constant provided immigration, mutation, and selection do not take place.

Har·dy-Wein·berg law

(hahr'dē wīn'bĕrg law) If mating occurs at random with respect to any one autosomal locus in a population in which the gene frequencies are equal in the two sexes, and the factors tending to change gene frequencies (mutation, differential selection, migration) are either absent or negligible, then in one generation the probabilities of all possible genotypes will on average equal the same proportions as if the genes were assembled at random. The law does not apply to two or more loci jointly, nor to X-linked traits where the initial gene frequencies differ in the two sexes.

Hardy-Weinberg law

a law stating that in a randomly mating large population the frequency of ALLELES will remain constant from generation to generation. Proposed in 1908 by G.H. Hardy in England and W. Weinberg in Germany, the law explains how the various alleles of a gene could remain constant in a population and yet be inherited by the rules of MENDELIAN GENETICS. The law shows why, for instance, dominant PHENOTYPES are not necessarily in excess of recessive ones in a population. If a gene has two alleles, A and a , with a frequency of p and q respectively, the genotypic frequencies would have the proportions:

This equation is derived from the BINOMIAL EXPANSION (p + q)² = 1.0. Such GENETIC EQUILIBRIUM only occurs under the following conditions: zero selection and mutation, no emigration or immigration, random mating and a large population size. However, selection pressures can produce stability (see GENETIC POLYMORPHISM and selection and mutation effects might cancel each other out.

Hardy,

Godfrey H., English mathematician, 1877-1947. Hardy-Weinberg equilibrium - the state in which the genetic structure of the population conforms to the prediction of the Hardy-Weinberg law. Synonym(s): random mating equilibriumHardy-Weinberg law - if mating occurs at random with respect to any one autosomal locus in a population in which the gene frequencies are equal in the two sexes, and the factors tending to change gene frequencies are absent or negligible, then in one generation the probabilities of all possible genotypes will on average equal the same proportions as if the genes were assembled at random.

Weinberg,

Wilhelm, German physician, 1862-1937. Hardy-Weinberg equilibrium - see under Hardy, Godfrey HHardy-Weinberg law - see under Hardy, Godfrey H

单词	hardy-weinberg law
释义	Hardy-Weinberg law Har·dy-Wein·berg law H0063950 (här′dē-wīn′bûrg)n. A fundamental principle in population genetics stating that the genotype frequencies and gene frequencies of a large, randomly mating population remain constant provided immigration, mutation, and selection do not take place. [After Godfrey Harold Hardy (1877-1947), British mathematician, and Wilhelm , Weinberg (1862-1937), German physician.] Hardy-Weinberg Law Hardy-Weinberg law [¦här·dē ′wīn‚bərg ‚lȯ] (genetics) The concept that frequencies of both genes and genotypes will remain constant from generation to generation in an idealized population where mating is random and evolutionary forces (such as mutation, migration, selection, or genetic drift) are absent. Hardy-Weinberg Law a law of population genetics that establishes the relationship between the frequencies of the genes and genotypes in a freely interbreeding population. The law was independently formulated in 1908 by the British mathematician G. Hardy and the German physician W. Weinberg. According to this law, if the number of diploid organisms in a population is so large that one may ignore occasional fluctuations in gene frequencies (that is, genetic drift), and in the absence of mutation, migration, and selection (with respect to the gene in question), the frequencies of genotypes AA, Aa, and aa in a given population, after the first generation, will remain the same in the succeeding generations. According to the Hardy-Weinberg formula, the frequencies of genotypes AA, Aa, and aa will be equal to p², 2pq, and q², respectively, where A and a represent the alleles of a gene that is not sex-linked, p represents the frequency of allele A, and q represents the frequency of allele a. The Hardy-Weinberg law also applies to multiallelic genes. In polyploid populations—as well as in the case of sex-linked genes in diploid populations—the relative proportions are only established over many generations. Even though a given population may conform to the Hardy-Weinberg formula, this is not necessarily proof that the population is unaffected by genetic processes. For example, the interbreeding of closely related individuals (that is, inbreeding), which increases the proportion of homozygotes in the population, when combined with selection against homozygotes may lead to genotype frequencies corresponding to the Hardy-Weinberg formula. By comparing the actually observed frequencies of genotypes to the frequencies theoretically expected according to the Hardy-Weinberg law, it is possible in a number of cases to gauge the frequencies of the alleles, to single out the factors influencing the alleles, and to obtain quantitative data pertaining, for example, to selection, non-random interbreeding, migration, and chance fluctuations. The concept of the genetic equilibrium of populations, as first expressed in the Hardy-Weinberg law, underlies the modern view of the interacting processes of population genetics. REFERENCES Timofeev-Resovskii, N. V., A. V. Iablokov, and N. V. Glotov. Ocherk ucheniia opopuliatsii. Moscow, 1973. Mettler, L., and T. Gregg. Genetika populiatsii i evoliutsiia. Moscow, 1972. (Translated from English.) Li, C. C. First Course in Population Genetics. California, 1975. L. A. ZHIVOTOVSKII See Hardy-Weinberg Law Hardy-Weinberg law Har·dy-Wein·berg law (har'dē wīn'bĕrg), if mating occurs at random with respect to any one autosomal locus in a population in which the gene frequencies are equal in the two sexes, and the factors tending to change gene frequencies (mutation, differential selection, migration) are either absent or negligible, then in one generation the probabilities of all possible genotypes will on average equal the same proportions as if the genes were assembled at random. The law does not apply to two or more loci jointly, nor to X-linked traits where the initial gene frequencies differ in the two sexes. Hardy-Weinberg law (här′dē-wīn′bûrg)n. A fundamental principle in population genetics stating that the genotype frequencies and gene frequencies of a large, randomly mating population remain constant provided immigration, mutation, and selection do not take place. Har·dy-Wein·berg law (hahr'dē wīn'bĕrg law) If mating occurs at random with respect to any one autosomal locus in a population in which the gene frequencies are equal in the two sexes, and the factors tending to change gene frequencies (mutation, differential selection, migration) are either absent or negligible, then in one generation the probabilities of all possible genotypes will on average equal the same proportions as if the genes were assembled at random. The law does not apply to two or more loci jointly, nor to X-linked traits where the initial gene frequencies differ in the two sexes. Hardy-Weinberg law a law stating that in a randomly mating large population the frequency of ALLELES will remain constant from generation to generation. Proposed in 1908 by G.H. Hardy in England and W. Weinberg in Germany, the law explains how the various alleles of a gene could remain constant in a population and yet be inherited by the rules of MENDELIAN GENETICS. The law shows why, for instance, dominant PHENOTYPES are not necessarily in excess of recessive ones in a population. If a gene has two alleles, A and a , with a frequency of p and q respectively, the genotypic frequencies would have the proportions: This equation is derived from the BINOMIAL EXPANSION (p + q)² = 1.0. Such GENETIC EQUILIBRIUM only occurs under the following conditions: zero selection and mutation, no emigration or immigration, random mating and a large population size. However, selection pressures can produce stability (see GENETIC POLYMORPHISM and selection and mutation effects might cancel each other out. Hardy, Godfrey H., English mathematician, 1877-1947. Hardy-Weinberg equilibrium - the state in which the genetic structure of the population conforms to the prediction of the Hardy-Weinberg law. Synonym(s): random mating equilibriumHardy-Weinberg law - if mating occurs at random with respect to any one autosomal locus in a population in which the gene frequencies are equal in the two sexes, and the factors tending to change gene frequencies are absent or negligible, then in one generation the probabilities of all possible genotypes will on average equal the same proportions as if the genes were assembled at random. Weinberg, Wilhelm, German physician, 1862-1937. Hardy-Weinberg equilibrium - see under Hardy, Godfrey HHardy-Weinberg law - see under Hardy, Godfrey H
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