Mendel, Gregor Johann

Mendel, Gregor Johann (1822-1884), Austrian monk, known as the father of modern genetics. He developed the principles of heredity by studying the variation and heredity of seven pairs of inherited characteristics in pea plants. Although the significance of his work was not recognized during his lifetime, it became the basis for the present day field of genetics.

Mendel was born on July 22, 1822, to a peasant family in Heinzendorf (now Hynčice, Czech Republic). He entered the Augustinian monastery at Brünn (now Brno, Czech Republic), which was known as a center of learning and scientific endeavor. He later became a substitute teacher at the technical school in Brünn. There Mendel became actively engaged in investigating variation, heredity, and evolution in plants at the monastery's experimental garden. Between 1856 and 1863 he cultivated and tested at least 28,000 pea plants, carefully analyzing seven pairs of seed and plant characteristics. His tedious experiments resulted in the enunciation of two generalizations that later became known as the laws of heredity (see Mendel's Laws). His observations also led him to coin two terms still used in present-day genetics: dominance, for a trait that shows up in an offspring; and recessiveness, for a trait masked by a dominant gene.

Mendel published his important work on heredity in 1866. Despite, or perhaps because of, its descriptions of large numbers of experimental plants, which allowed him to express his results numerically and subject them to statistical analysis, this work made virtually no impression for the next 34 years. Only in 1900 was his work recognized more or less independently by three investigators, one of whom was the Dutch botanist Hugo Marie de Vries, and not until the late 1920s and the early '30s was its full significance realized, particularly in relation to evolutionary theory. As a result of years of research in population genetics, investigators were able to demonstrate that Darwinian evolution can be described in terms of the change in gene frequency of Mendelian pairs of characteristics in a population over successive generations.

Mendel's later experiments with the hawkweed Hieracium proved inconclusive, and because of the pressure of other duties he ceased his experiments on heredity by the 1870s. He died in Brünn on January 6, 1884.

Astrophysics

Astrophysics, the branch of astronomy that seeks to understand the birth, evolution, and end states of celestial objects and systems in terms of the physical laws that govern them. For each object or system under study, astrophysicists observe radiations emitted over the entire electromagnetic spectrum and variations of these emissions over time (see Electromagnetic Radiation; Spectroscopy; Spectrum). This information is then interpreted with the aid of theoretical models. It is the task of such a model to explain the mechanisms by which radiation is generated within or near the object, and how the radiation then escapes. Radiation measurements can be used to estimate the distribution and energy states of the atoms, as well as the kinds of atoms, making up the object. The temperatures and pressures in the object may then be estimated using the laws of thermodynamics.

Steady-State Theory

Steady-State Theory, theory of cosmology, or the study of the universe and its origins, that was once a rival to the big bang theory, which proposes that the universe was created in a giant explosion. The steady-state theory holds that the universe looks, on the whole, the same at all times and places. The Austrian-British astronomer Hermann Bondi and the Austrian-American astronomer Thomas Gold formulated the theory in 1948. The British astronomer Fred Hoyle soon published a different version of the theory based on his mathematical understanding of the problem. Most astronomers believe that astronomical observations contradict the predictions of the steady-state theory and uphold the big bang theory.

Gold, Thomas

Gold, Thomas (1920- ), Austrian-American astronomer, born in Vienna and educated at the University of Cambridge. He is best known as the developer—with Austrian-British mathematician Hermann Bondi and British astronomer Fred Hoyle—of the steady-state theory of the universe. The theory, proposed in 1948, holds that the universe is homogeneous and that matter is continuously being created as the universe expands. Most scientists currently endorse the big-bang theory instead. Gold also developed the accepted explanation of pulsars as being spinning neutron stars.

Spectroscopy

Spectroscopy, in physics and physical chemistry, the study of spectra (see Spectrum). The basis of spectroscopy is that each chemical element has its own characteristic spectrum. This fact was recognized in 1859 by German scientists Gustav Robert Kirchhoff and Robert Wilhelm Bunsen. They developed the prism spectroscope in its modern form and applied it to chemical analysis. One of two principal spectroscope types, this instrument consists of a slit for admitting light from an external source, a group of lenses, a prism, and an eyepiece. Light that is to be analyzed passes through a collimating lens, which makes the light rays parallel, and the prism; then the image of the slit is focused at the eyepiece. One actually sees a series of images of the slit, each a different color, because the light has been separated into its component colors by the prism. The German scientists were the first to recognize that characteristic colors of light, or the spectra, are emitted and absorbed by particular elements.