Balanced polymorphism The maintenance of two or more alleles in a population due to the selective advantage of the heterozygote. A heterozygote is a genotype consisting of two different alleles of a gene for a particular trait (Aa). Balanced polymorphism is a type of polymorphism where the frequencies of the coexisting forms do not change noticeably over many generations. Polymorphism is a genetic trait controlled by more than one allele, each of which has a frequency of 1 percent or greater in the population gene pool. Polymorphism can also be defined as two or more phe-notypes maintained in the same breeding population.
Banting, Frederick Grant (1891-1941) Canadian Physician Frederick Grant Banting was born on November 14, 1891, at Alliston, Ontario, Canada, to William Thompson Banting and Margaret Grant.
He went to secondary school at Alliston and then to the University of Toronto to study divinity before changing to the study of medicine. In 1916 he took his M.B. degree and joined the Canadian Army Medical Corps and served in France during World War I. In 1918 he was wounded at the battle of Cambrai, and the following year he was awarded the Military Cross for heroism under fire.
In 1922 he was awarded his M.D. degree and was appointed senior demonstrator in medicine at the university of Toronto. In 1923 he was elected to the Banting and Best Chair of Medical Research, which had been endowed by the legislature of the Province of Ontario.
Also in 1922, while working at the university of Toronto in the laboratory of the Scottish physiologist John James Richard macleod, and with the assistance of the Canadian physiologist Charles Best, Banting discovered insulin after extracting it from the pancreas. The following year he received the Nobel Prize in medicine along with Macleod. Angered that Macleod, rather than Best, had received the Nobel Prize, Banting divided his share of the award equally with Best. It was Canada’s first Nobel Prize. He was knighted in 1934. The word banting was associated with dieting for many years.
In February 1941 he was killed in an air disaster in Newfoundland.
Barany, Robert (1876-1936) Austrian Physician Robert Barany was born on April 22, 1876, in Vienna, the eldest son of the manager of a farm estate. His mother, Maria Hock, was the daughter of a well-known Prague scientist. The young Barany contracted tuberculosis, which resulted in permanent knee problems.
He completed medical studies at vienna university in 1900, and in 1903, he accepted a post as demonstrator at the ontological clinic.
Barany developed a rotational method for testing the middle ear, known as the vestibular system, that commands physical balance by integrating an array of neurological, biological, visual, and cognitive processes to maintain balance. The middle ear’s vestibular system is made up of three semicircular canals and an otolith. Inside the canals are fluid and hairlike cilia that register movement. As the head moves, so does the fluid, which in turn moves the cilia that send signals to the brain and nervous system. The function of the otolith, a series of calcium fibers that remain oriented to gravity, is similar. Both help the body to stay upright. Barany’s contributions in this area won him the Nobel Prize in physiology in 1914. To receive his award, he had to be released from a Russian prisoner of war camp in 1916 at the request of the prince of Sweden.
After the war he accepted the post of principal and professor of the Otological Institute in Uppsala, where he remained for the remainder of his life.
During the latter part of his life, Barany studied the causes of muscular rheumatism. Although he suffered a stroke, this did not prevent him from writing on the subject. He died at Uppsala on April 8, 1936. An elite organization called the Barany Society is named after him and is devoted to vestibular research.
Barchan A crescent-shaped dune with wings, or horns, pointing downwind.
Bark The outer layer or "skin" of stems and trunks that forms a protective layer. It is composed of all the tissues outside the vascular cambium in a plant growing in thickness. Bark consists of phloem, phelloderm, cork cambium, and cork.
Barr body One of the two X chromosomes in each somatic cell of a female is genetically inactivated. The Barr body is a dense object or mass of condensed sex chromatin lying along the inside of the nuclear envelope in female mammalian cells; it represents the inactivated X chromosome. X inactivation occurs around the 16th day of embryonic development. Mary Lyon, a British cytogeneticist, introduced the term Barr body.
Basal body (kinetosome) A eukaryotic cell organelle within the cell body where a flagellum arises, which is usually composed of nine longitudinally oriented, equally spaced sets of three microtubules. They usually occur in pairs and are structurally identical to a centriole.
Not to be confused with basal body temperature (BBT), which is the lowest body temperature of the day, usually the temperature upon awakening in the morning. BBT is usually charted daily and is used to determine fertility or to achieve pregnancy.
Basal metabolic rate (BMR) BMR is the number of calories your body burns at rest to maintain normal body functions and changes with age, weight, height, gender, diet, and exercise.
Base A substance that reduces the hydrogen ion concentration in a solution. A base has less free hydrogen ions (H+) than hydroxyl ions (OH-) and has a pH of more than 7 on a scale of 0-14. A base is created when positively charged ions (base cations) such as magnesium, sodium, potassium, and calcium increase the pH of water when released to solution. They have a slippery feel in water and a bitter taste. A base will turn red litmus paper blue (acids turn blue litmus red). The three types of bases are: Arrhenius, any chemical that increases the number of free hydroxide ions (OH-) when added to a water-based solution; Bronsted or Bronsted-Lowry, any chemical that acts as a proton acceptor in a chemical reaction; and Lewis, any chemical that donates two electrons to form a covalent bond during a chemical reaction. Bases are also known as alkali or alkaline substances, and when added to acids they form salts. Some common examples of bases are soap, ammonia, and lye.
An example of a deflation zone (low ground behind fore dunes) and an example of barchan dunes in Morro Bay, California.
Basement membrane The thin extracellular layer composed of fibrous elements, proteins, and space-filling molecules that attaches the epithelium tissue (which forms the superficial layer of skin and some organs and the inner lining of blood vessels, ducts, body cavities, and the interior of the respiratory, digestive, urinary, and reproductive systems) to the underlying connective tissue. It is made up of a superficial basal lamina produced by the overlying epithelial tissue, and an underlying reticular lamina, which is the deeper of two layers and produced by the underlying connective tissue. It is the layer of tissue that cells "sit" or rest on.
Base pairing The specific association between two complementary strands of nucleic acids that results from the formation of hydrogen bonds between the base components (adenine [A], guanine [G], thymine [T], cytosine [C], uracil [U] of the nucleotides of each strand (the lines indicate the number of hydrogen bonds):
Single-stranded nucleic acid molecules can adopt a partially double-stranded structure through intrastrand base pairing.
Base-pair substitution There are two main types of mutations within a gene: base-pair substitutions and base-pair insertions or deletions. A base-pair substitution is a point mutation; it is the replacement of one nucleotide and its partner from the complementary deoxyribonucleic acid (DNA) strand with another pair of nucleotides. Bases are one of five compounds—ade-nine, guanine, cytosine, thymine, and uracil—that form the genetic code in DNA and ribonucleic acid (RNA).
Basidiomycetes A group of fungi whose sexual spores (basidiospores) are borne in a basidium, a club-shaped reproductive cell. Includes the orders Agaricales (mushrooms) and Aphyllophorales.
Basidium (plural, basidia) A specialized club-shaped sexual reproductive cell found in the fertile area of the hymenium, the fertile sexual spore-bearing tissues of all basidiomycetes, and that produces sexual spores on the gills of mushrooms. Shaped like a baseball bat, it possesses four slightly inwardly curved horns or spikes called sterigma on which the basid-iospores are attached.
Batesian mimicry A type of mimicry described by H. W. Bates in 1861 that describes the condition where a harmless species, the mimic, looks like a different species that is poisonous or otherwise harmful to predators, the model, and in this way gains security and protection by counterfeiting its appearance. Since many predators have become sick from eating a poisonous animal, they will avoid any similar looking animals in the future. Examples of Batesian mimicry include the Viceroy mimicking the Monarch butterfly and the clearwing moth that resembles a bee by having yellow and black coloring.
Bathyal zone The deepest part of the ocean where light does not penetrate.
B cell or lymphocyte A type of white blood cell, or lymphocyte, that makes up 25 percent or more of the white blood cells in the body. The other class of lymphocyte is T cells. B cells develop in the bone marrow and spleen, and during infections they are transformed into plasma cells that produce large quantities of antibody (immunoglobulin) directed at specific pathogens. A cancer of the B lymphocytes is called a B-cell lymphoma.
Behavioral ecology A subdiscipline that seeks to understand the functions, or fitness consequences, of behavior in which animals interact with their environment.
Bekesy, Georg von (1899-1972) Hungarian Physicist Georg von Bekesy was born in Budapest, Hungary, on June 3, 1899, to Alexander von Bekesy, a diplomat, and his wife Paula. He received his early education in Munich, Constantinople, Budapest, and in a private school in Zurich. He received a Ph.D. in physics in 1923 from the University of Budapest for a method he developed for determining molecular weight. He began working for the Hungarian Telephone and Post Office Laboratory in Budapest until 1946. During the years 1939-46 he was also professor of experimental physics at the University of Budapest.
The Monarch butterfly is a chemically protected species that is mimicked by the Viceroy. This is known as Batesian mimicry.
While his research was concerned mainly with problems of long-distance telephone transmission, he conducted the study of the ear as a main component of the transmission system. He designed a telephone earphone and developed techniques for rapid, nondestructive dissection of the cochlea.
In 1946 he moved to Sweden as a guest of the Karolinska Institute and did research at the Technical Institute in Stockholm. Here he developed a new type of audiometer. The following year he moved to the United States to work at Harvard University in the Psycho-Acoustic Laboratory and developed a mechanical model of the inner ear. He received the Nobel Prize in 1961 for his discoveries concerning the physical mechanisms of stimulation within the cochlea. He moved on to the University of Hawaii in 1966, where a special laboratory was built for him.
He received numerous honors during his lifetime. He died on June 13, 1972, in Honolulu.
Benthic zone A lower region of a freshwater or marine body. It is below the pelagic zone and above the abyssal zone, which is the benthic zone below 9,000 m. Organisms that live on or in the sediment in these environments are called benthos.
Beringia All of the unglaciated area that encompassed northwestern North America and northeastern Asia, including the Bering Strait, during the last ice age.
Berry A pulpy and stoneless fruit containing one or more seeds, e.g., strawberry.
Beta sheet Preferentially called a beta pleated sheet; a regular structure in an extended polypeptide chain, stabilized in the form of a sheet by hydrogen bonds between CO and NH groups of adjacent (parallel or antiparallel) chains.
Beta strand Element of a beta sheet. One of the strands that is hydrogen bonded to a parallel or antiparallel strand to form a beta sheet.
Beta turn A hairpin structure in a polypeptide chain reversing its direction by forming a hydrogen bond between the CO group of amino acid residue n with the NH group of residue (n+3). See also helix.
Biennial A plant that requires two years or at least more than one season to complete its life cycle. In the first year, plants form vegetative growth, and in the second year they flower. (Latin biennialis, from biennis; bis, twice, and annus, year)
Bifunctional ligand A ligand that is capable of simultaneous use of two of its donor atoms to bind to one or more central atoms. See also ambidentate.
Bilateral symmetry Characterizing a body form having two similar sides—one side of an object is the mirror image of its other half—with definite upper and lower surfaces and anterior and posterior ends. Also called symmetry across an axis.
In plants, the term applies to flowers that can be divided into two equal halves by only one line through the middle. Most leaves are bilaterally symmetrical.
Bilateria Members of the branch of eumetazoans possessing bilateral symmetry. Many bilaterian animals exhibit cephalization, an evolutionary trend toward concentration of sensory structures, mouth, and nerve ganglia at the anterior end of the body. All bilaterally symmetrical animals are triploblastic, that is, having three germ layers: ectoderm, endoderm, and mesoderm.
Amoeba proteus showing cell division via binary fission. Amoebas are protozoans, the simplest form of animal life.
Binary fission A type of asexual reproduction in prokaryotes (cells or organisms lacking a membrane-bound, structurally discrete nucleus and other subcellu-lar compartments) in which a cell divides or splits into two "daughter" cells, each containing a complete copy of the genetic material of the parent. Examples of organisms that reproduce this way are bacteria, paramecium, and Schizosaccharomyces pombe (an ascomycetous species of yeast). Also known as transverse fission.
Binding site A specific region (or atom) in a molecular entity that is capable of entering into a stabilizing interaction with another molecular entity. An example of such an interaction is that of an active site in an enzyme with its substrate. Typical forms of interaction are by hydrogen bonding, coordination, and ion-pair formation. Two binding sites in different molecular entities are said to be complementary if their interaction is stabilizing.