A condition under which the genotypic frequencies in a diploid population are equal to the products of the allele frequencies involved.

The steady-state relationship between relative frequencies of two or more alleles in an idealized population; both the allele frequencies and the genotype frequencies will remain constant from generation to generation in a population breeding at random in the absence of evolutionary forces. Hardy-Weinberg theorem An axiom maintaining that the sexual shuffling of genes alone cannot alter the overall genetic makeup of a population. haustorium pl. haustoria In parasitic fungi, a nutrient-absorbing hyphal tip that penetrates the tissues of the host but remains outside the host cell membranes. Haversian system(ha- ver-shun) One of many structural units of vertebrate bone, consisting of concentric layers of mineralized bone matrix surrounding lacunae, which contain osteocytes, and a central canal, which contains blood vessels and nerves.

a mathematical model of genetic equilibrium: p2 + 2pq + q2 = 1.

State in which the allele and genotype frequencies do not change from one generation to the next in a population. It requires random mating and the absence of selection, mutation, migration, and genetic drift. In Hardy-Weinberg equilibrium, allele and genotype frequencies are related through the Hardy-Weinberg law: for a locus with two alleles P, Q at frequencies and respectively, homozygotes for P are found at frequency , homozygotes for Q have a frequency 2, and heterozygotes are found at a frequency 2pq. Although conditions for Hardy-Weinberg equilibrium are seldom strictly met, genotype frequencies are usually consistent with the Hardy-Weinberg law. Some useful software packages to test whether a set of genotypic frequencies conforms to Hardy-Weinberg are Arlequin ( http://anthropologie.unige.ch/arlequin/) and Genepop ( http://wbiomed.curtin.edu.au/genepop/), among others.

In an infinitely large population, gene and genotype frequencies remain stable as long as there is no selection, mutation, or migration. For a bi-allelic locus where the gene frequencies are p and q: p2+2pq+q2 = 1 (Online HWE Analysis; lectures on HWE: 1 & 2).

The frequencies of genotypes at a locus resulting from random mating at that locus; for two alleles, 1 and 2, with respective frequencies and , the Hardy-Weinberg equilibrium frequencies are 1, 2 pq 2. Despite the simplifying assumptions required to predict these frequencies, most loci in most populations are in Hardy-Weinberg equilibrium. Thus the Hardy-Weinberg law, which predicts these frequencies, is one of the great unifying themes of biology.

a state attained by a population which displays constant gene and genotype frequencies from generation to generation. In the case of a locus with two alleles, A and B, occuring at frequencies p and q, respectively, the frequency of genotype AA is p2, the frequency of AB is 2pq and the frequency of BB is q2. The population in H-W equilibrium has to be large, random-mating with no selection, mutation, or migration.

A condition under which the genotype frequencies in a diploid population are equal to the products of their allele frequencies.

In an effectively infinite and panmictic population and in the absence of mutation and natural selection, the frequency of any given allele will change until it reaches a stable predictable value in the population, and then remain there.

After one generation of random mating, the single-locus genotypic frequencies in a population can be represented as a binomial (with two alleles) or multinomial (with multiple alleles) function of the allelic frequencies for that locus.

The maintenance of allele frequencies in a population with random mating and absence of selection.