Visual discovery of chromosomes. Textbooks have often said that chromosomes were first observed in plant cells by a Swiss botanist named Karl Wilhelm von Nägeli in 1842.[1] However, this opinion has been challenged, perhaps decisively, by Henry Harris, who has freshly reviewed the primary literature.[2] In his opinion the claim of Nägeli to have seen spore mother cells divide is mistaken, as are some of his interpretations. Harris considers other candidates, especially Wilhelm Hofmeister, whose publications in 1848-9 include plates which definitely show mitotic events.[3][4] Hofmeister was also the choice of Cyril Darlington. The work of other cytologists such as Walther Flemming, Eduard Strasburger, Otto Bütschli, Oskar Hertwig and Carl Rabl should definitely be acknowledged. The use of basophilic aniline dyes was a new technique for effectively staining the chromatin material in the nucleus. Their behavior in animal (salamander) cells was later described in detail by Walther Flemming, who in 1882 "provided a superb summary of the state of the field".[5][6] The name chromosome was invented in 1888 by Heinrich von Waldeyer. However, van Beneden's monograph of 1883 on the fertilised eggs of the parasitic roundworm Ascaris megalocephala was the outstanding work of this period.[7] His conclusions are classic: * Thus there is no fusion between the male chromatin and the female chromatin at any stage of division... * The elements of male origin and those of female origin are never fused together in a cleavage nucleus, and perhaps they remain distinct in all the nuclei derived from them. [tranl: Harris p162] "It is not easy to identify who first discerned chromosomes during mitosis, but there is no doubt that those who first saw them had no idea of their significance... [but] with the work of Balbiani and van Beneden we move away from... the mechanism of cell division to a precise delineation of chromosomes and what they do during the division of the cell." [8] Van Beneden's master work was closely followed by that of Carl Rabl, who reached similar conclusions. [9] This more or less concludes the first period, in which chromosomes were visually sighted, and the morphological stages of mitosis were described. Coleman also gives a useful review of these discoveries.[10] Nucleus as the seat of heredity. The origin of this epoch-making idea lies in a few sentences tucked away in Ernst Haeckel's Generelle Morphologie of 1866.[11] The evidence for this insight gradually acumulated until, after twenty or so years, two of the greatest in a line of great German scientists spelt it out. August Weismann proposed that the germ line was separate from the soma, and that the cell nucleus was the repository of the hereditary material, which he proposed was arranged along the chromosomes in a linear manner. Furthermore, he proposed that at fertilisation a new combination of chromosomes (and their hereditary material) would be formed. This was the explanation for the reduction division of meiosis (first described by van Beneden). Chromosomes as vectors of heredity. In a series of outstanding experiments, Theodor Boveri gave the definitive demonstration that chromosomes were the vectors of heredity. His two principles were: : The continuity of chromosomes : The individuality of chromosomes. It was the second of these principles which was so original. He was able to test the proposal put forward by Wilhelm Roux, that each chromosome carries a different genetic load, and showed that Roux was right. Upon the rediscovery of Mendel, Boveri was able to point out the connection between the rules of inheritance and the behaviour of the chromosomes. It is interesting to see that Boveri influenced two generations of American cytologists: Edmund Beecher Wilson, Walter Sutton and Theophilus Painter were all influenced by Boveri (Wilson and Painter actually worked with him). In his famous textbook The Cell, Wilson linked Boveri and Sutton together by the Boveri-Sutton theory. Mayr remarks that the theory was hotly contested by some famous geneticists: William Bateson, Wilhelm Johannsen, Richard Goldschmidt and T.H. Morgan, all of a rather dogmatic turn of mind. Eventually complete proof came from chromosome maps - in Morgan's own lab! [12]
Camillo Golgi who was Italian is one of the most famous cytologists. His contribution includes his investigations into the fine structure of the nervous system.
There are many famous cytologists such as Leuwenhoek,Peter Mitchel,Micheal Schwann,Palade, Robert Hook etc
Darwin's contribution was the theory of natural selection that explained the mechanism behind evolution.
How should I know! >:P
cytologist and thier contributions
Camillo Golgi who was Italian is one of the most famous cytologists. His contribution includes his investigations into the fine structure of the nervous system.
not organic
cytologists
Cytology is the study of cells, so therefore, a Cytologists main area of study would be the Cellular level. :)
Cell biologists or sometimes cytologists.
CYTOLOGISTS and others commonly refer to parthenogenesis as asexual reproduction.
net contribution is contribution from customers while net profit is from all expenses deducted
There are many famous cytologists such as Leuwenhoek,Peter Mitchel,Micheal Schwann,Palade, Robert Hook etc
A contribution margin income statement is an income statement in which all variable expenses are deducted from sales to arrive at a contribution margin. It is the expanded version.
Well, he ate all the pies.
all i know is that Greece created democracy
to make the world about the world