Laboratory technique used to make numerous copies of specific DNA segments quickly and accurately. These are needed for various experiments and procedures in molecular biology, forensic analysis (DNA fingerprinting), evolutionary biology (to amplify DNA fragments found in ancient specimens), and medicine (to diagnose genetic disease or detect low viral counts). Invented by Kary Mullis, PCR requires a DNA template (as little as one molecule) to copy, nucleotides to build the copies, and the enzyme DNA polymerase to catalyze the formation of bonds between the nucleotide monomers. Each three-step cycle (separating the two strands of the DNA double helix, marking the ends of the segment to be copied, and catalyzing the formation of bonds), which takes only minutes to complete, doubles the number of DNA strands present in the reaction medium. Repetition of this cycle many times results in an exponential increase in the amount of DNA.
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Sequence of transfer of matter and energy from organism to organism in the form of food. These interconnected feeding relationships intertwine locally into a food web because most organisms consume or are consumed by more than one other type of organism. Plants and other photosynthetic organisms (such as phytoplankton), which convert solar energy to food, are the primary food source. In a predator chain, a plant-eating animal is eaten by a larger animal. In a parasite chain (see parasitism), a smaller organism consumes part of a larger host and may itself be parasitized by even smaller organisms. In a saprophytic chain, microorganisms live on dead organic matter. Because energy, in the form of heat, is lost at each step, or trophic level, chains do not normally encompass more than four or five trophic levels.
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Process yielding products that initiate further processes of the same kind. Nuclear chain reactions are a series of nuclear fissions initiated by neutrons produced in a preceding fission. A critical mass, large enough to allow more than one fission-produced neutron to be captured, is necessary for the chain reaction to be self-sustaining. Uncontrolled chain reactions, as in an atomic bomb, occur when large numbers of neutrons are present and the reactions multiply very quickly. Nuclear reactors control their reactions through the careful distribution of the fissionable material and insertion of neutron-absorbing materials.
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Turkish coat of chain mail, 16th century
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There were 64 households out of which 9.4% had children under the age of 18 living with them, 57.8% were married couples living together, 3.1% had a female householder with no husband present, and 37.5% were non-families. 32.8% of all households were made up of individuals and 23.4% had someone living alone who was 65 years of age or older. The average household size was 1.98 and the average family size was 2.48.
In the village the population was spread out with 13.4% under the age of 18, 0.8% from 18 to 24, 15.7% from 25 to 44, 30.7% from 45 to 64, and 39.4% who were 65 years of age or older. The median age was 59 years. For every 100 females there were 86.8 males. For every 100 females age 18 and over, there were 96.4 males.
The median income for a household in the village was $25,714, and the median income for a family was $29,375. Males had a median income of $14,583 versus $14,545 for females. The per capita income for the village was $14,944. There were 3.2% of families and 7.8% of the population living below the poverty line, including 21.4% of under eighteens and none of those over 64.