With the formation of cytology as a separate branch of biology
favourable conditions were created for its accelerated development and
improvement of the methods existing at that time, and the introduction of
new, more sophisticated ones. Such is microscopy for example.
Alongside ordinary light microscopy other types such as phase-contrast,
interference, polarization, fluorescent and electron microscopies have
gradually been created and applied. X-ray diffraction analysis has proven
very precious in the studies on high-molecular substances (proteins,
nucleic acids, carbohydrates) playing a decisive role in the structure and
function of the cell.
Discovery of the Discrete Factors of Heredity. The Experiments of Gregor Mendel
Section 2.4.
Heredity as a phenomenon has been known since antiquity. People have
noticed the similarities between parents and children and have practised
selection of animals and plants according to the qualities preferred. But the
material basis of this phenomenon and the mechanisms involved in it have
remained completely in the dark till the beginning of the XX century.
This problem has been occupying scientist minds for a long time. It was
considered that heredity in some way was transmitted through blood. Darvin’s
suggestion about the existence of discrete hereditary units in the blood of
animals and men called gemules by him is well-known. His cousin F. Galton
has expressed disagreement with that opinion being based on the “simple”
fact that transfusions of blood from white rabbits into black ones and vice
versa did not lead to a change in their colouring.
In 1865 the studious monk Gregor Mendel has discovered some
regularities in the inheritance of parental characteristic features in the process of
hybridization of peas (Pisum sativum). His work “Experiments on Plant-Hybrids”
(Mendel, 1866) has remained unnoticed. The symbols provided by him to
designate the hereditary factors and the “boring” figures of the results obtained
could not have possibly interested his contemporaries. Scientific thought at that
time was not mature enough to accept his results and give him his due. His work
has become known to the public after 1900, when C. Correns, H. de Vries and
E. Tschermak have indenpendently from one another rediscovered these
regularities. After Dobzhansky’s view (1955) “The work of Mendel is truly classic
and will be studied by all students of genetics as a brilliant example of the
application of scientific methods in modern experimental science”.
Mendel’s success was ensured by the combination of his skill to select
the exact object for studies, to choose well-discernible, contrasting and
quite simple hereditary features, to lead precisely the experiments and to
interpret the results correctly implementing mathematico-statistical
processing.