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Joseph Grafton Gall (April 14, 1928 – September 12, 2024) was an American cell biologist whose studies revealed many details of chromosome structure and function. Gall's studies were greatly facilitated by his knowledge of many different organisms because he could select the most favorable organism to study when approaching a specific question about nuclear structure.
Theophilus Painter (1889–1969), US zoologist, studied fruit fly and human testis chromosomes; Arthur Pardee (1921–2019), US scientist who discovered restriction point in the cell cycle; Mary-Lou Pardue, American geneticist at MIT; Klaus Patau (1908–1975), German-American cytogeneticist, described trisomy 13
The DNA double helix structure proposed by Watson and Crick was based upon "Watson-Crick" bonds between the four bases most frequently found in DNA (A, C, T, G) and RNA (A, C, U, G). However, later research showed that triple-stranded, quadruple-stranded and other more complex DNA molecular structures required Hoogsteen base pairing.
In the 1940s and early 1950s, experiments pointed to DNA as the portion of chromosomes (and perhaps other nucleoproteins) that held genes. A focus on new model organisms such as viruses and bacteria, along with the discovery of the double helical structure of DNA in 1953, marked the transition to the era of molecular genetics.
1903: Walter Sutton and Theodor Boveri independently hypothesizes that chromosomes, which segregate in a Mendelian fashion, are hereditary units; [6] see the chromosome theory. Boveri was studying sea urchins when he found that all the chromosomes in the sea urchins had to be present for proper embryonic development to take place.
Friedrich Miescher (1844–1895) discovered a substance he called "nuclein" in 1869. Somewhat later, he isolated a pure sample of the material now known as DNA from the sperm of salmon, and in 1889 his pupil, Richard Altmann, named it "nucleic acid". This substance was found to exist only in the chromosomes.
Human DNA recovered from remains found in Europe is revealing our species’ shared history with Neanderthals. The trove is the oldest Homo sapiens DNA ever documented, scientists say.
Location of eukaryote nuclear DNA within the chromosomes. DNA usually occurs as linear chromosomes in eukaryotes, and circular chromosomes in prokaryotes. The set of chromosomes in a cell makes up its genome; the human genome has approximately 3 billion base pairs of DNA arranged into 46 chromosomes. [96]