Archaea: A unique group of microorganisms that are called bacteria (Archaeobacteria) but are genetically and metabolically different from all other known bacteria. They appear to be living fossils, the survivors of an ancient group of organisms that bridged the gap in evolution between bacteria and multicellular organisms (eukaryotes).
Archaeogenetics: The study of the past using the techniques of molecular genetics. The application of genetics to archeology. The term “archaeogenetics” was coined in the 1990s by the archeologist Colin Renfrew from the Greek archaios (ancient) + genetics = archaeogenetics, literally, ancient genetics. In archaeogenetics, information on the DNA of different ethnic groups from around […]
Archaeology: The scientific study of the material remains of past peoples. In archaeology today, a range of biological techniques, including DNA analysis, enter into what has been termed bioarchaeology.
- Arcuate neuron
Arcuate neuron: A neuron in the arcuate nucleus of the brain. See: Arcuate nucleus.
- Arcuate nucleus
Arcuate nucleus: A collection of neurons (nerve cells) in the hypothalamus of the brain. Some arcuate neurons contain dopamine and act to inhibit the release of the hormone prolactin by the pituitary gland. Other arcuate neurons contain a substance called neuropeptide Y (NPY) and influence hunger. When activated, these neurons can produce remarkable increases in […]
- Arcus senilis
Arcus senilis: A cloudy opaque arc or circle around the edge of the eye, often seen in the eyes of the elderly.