The terms chromosome and gene were used long before biologists really understood what these structures were. When the Austrian monk and biologist Gregor Mendel (1822–1884) developed the basic ideas of heredity, he assumed that genetic traits were somehow transmitted from parents to offspring in some kind of tiny "package." That package was later given the name "gene." When the term was first suggested, no one had any idea as to what a gene might look like. The term was used simply to convey the idea that traits are transmitted from one generation to the next in certain discrete units.
Magnification of chromosome 17, which carries the breast and ovarian cancer gene. (Reproduced by permission ofCustom Medical Stock Photo, Inc.)
The term "chromosome" was first suggested in 1888 by the German anatomist Heinrich Wilhelm Gottfried von Waldeyer-Hartz (1836–1921). Waldeyer-Hartz used the term to describe certain structures that form during the process of cell division (reproduction).
One of the greatest breakthroughs in the history of biology occurred in 1953 when American biologist James Watson (1928– ) and English chemist Francis Crick (1916– ) discovered the chemical structure of a class of compounds known as deoxyribonucleic acids (DNA). The Watson and Crick discovery made it possible to express biological concepts (such as the gene) and structures (such as the chromosome) in concrete chemical terms.
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When unspecialized stem cells give rise to specialized cells, the process is called differentiation. ... The interaction of signals during differentiation causes the cell's DNA to acquire epigenetic marks that restrict DNA expression in the cell and can be passed on through cell division
The primary function of the carbon cycle is to recycle the supply of carbon on Earth.
