WHAT IS CLASSICAL AND MOLECULAR GENETICS

Genetics began somewhat more than a hundred years ago and was based on the following observations:

Individual organisms which belong to the same species have by and large the same characteristics, but they may differ from one

another as far as certain details are concerned.

 A dog, for example, is always a dog, but there are obviously different breeds because of their outward appearances (phenotypes) differ.

If the same characteristic is found in parents and their progeny, the latter have inherited it.

Classical genetics deals with the natural laws that

govern this heredity.

Chromosomes were identified as the carriers of inheritance information.

 In higher forms of life, these chromosomes are packed in the cell nucleus.

Research in classical genetics is firstly concerned with individual organisms that differ from the standard and exhibit a transmissible outward form, such as flowers with abnormal colours.

Such variants are attributed to changes in the inheritance information (mutations).

 By crossing independent mutants, geneticists can determine the part of a chromosome on which the change is located.

Such experiments are used to produce so-called gene maps showing on which part of a chromosome a characteristic, or a gene responsible for this characteristic, is located.

This does not reveal anything, however, about the chemical nature of the transmission.

This puzzle was solved about fifty years ago:

it was proved through experiments with bacteria that a so-called nucleic acid is an inheritance information carrier in chromosomes.

It is now known by the abbreviation DNA.

 Shortly after-wards Francis Crick and James Watson also described the structure of DNA as an extremely long and very thin thread molecule.

Owing to its appearance, DNA was also described as a double helix.

A gene, i.e. an inherited characteristic corresponds to a short segment of the long genetic constitution thread.

The discovery of the chemical nature of genetic make-up was followed by the development of molecular genetics or the study of genes and their activities.

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