The Pre-Mendelian Era and Mendelism | Genetics

In this article we will discuss about the pre-mendelian era birth of mendelism.

Pre-Mendelian Era:

Man’s curiosity to know about transmission of hereditary characters is as old as humanity itself. From the earliest times it had been noticed that the offspring may resemble their parents, grandparents, or other relations. Around 300 BC the great Aristotle had observed that peculiarities of hair, nails and even gait may reappear in offspring, that characters not visible in an individual may also be inherited.

It appears that the existence of heredity was taken for granted. Yet, the rules which govern transmission of characters were not understood. Explanations were sought everywhere, even in the prevailing beliefs of the time such as magic, witchcraft, gods and folklore.

Many considered heredity to be some sort of a blending process, because of which the offspring showed different “dilutions” of the parental characteristics. The concept of blending inheritance fitted well with ancient thinking as it could explain why some children were more like their parents whereas others were less.

As far back as 400 BC an ancient Greek writer suggested the role of environment in producing variations in inheritance. The idea appears similar to the “Theory of acquired characteristics” proposed by Lamarck twenty-two centuries later.

The earliest indications about the material basis of heredity came from plant breeding procedures practiced by farmers who were aware of various techniques of hybridisation and selection for developing new varieties.

In the middle of the eighteenth century Carolus Lin­naeus (1707-1778) a Swedish taxonomist, and two German plant breeders Josef Gottlieb Kolreuter (1733-1806) and Karl Friedrich Von Gaertner (1722-1850) performed artificial cross pollinations in plants and obtained hybrid offspring.

In 1760 Kolreuter published a book in which he described 500 plant hybridisation experiments. Although his observations were similar to those of Mendel, he was not able to interpret them correctly. For example, in the cross between Nicotiana rustica and N. paniculata he could not understand the vigorous and sterile nature of the hybrid offspring.

Gaertner carried out similar experiments on garden peas, the very material which Mendel studied successfully a few decades later. In crosses of maize plants Gaertner found that if one parent has red kernels the other yellow, the hybrids were all of the yellow type. When these hybrids were self fertilised the second generation showed roughly three yellow to one red plant—identical to the 3: 1 ratio found later by Mendel.

It was about the same time, in the first quarter of the nineteenth century that three British botanists, Knight, Seton and Goss were also experimenting with inheritance of seed color in garden peas. They observed that a cross between plants with yellow seeds and green seeds produced all yellow seeded plants in the first generation.

On self fertilisation they obtained second generation offspring with both yellow and green seeds. Plants with green seeds on self fertilisation produced only green seeded offspring showing that green seed colour always breeds true.

The works of all the plant hybridisers were studied and analysed in detail by Mendel. It is noteworthy that most of the important concepts of Genetics emerged on the basis of classical experiments done on plants. Among animals, efforts of scientists were focused on the study of mode of sexual reproduction. Spallanzani in 1785 obtained offspring from artificial insemination of dogs.

In 1875 Oscar Hertwig observed that in sea urchins, fertilisation involves the union of sperm nucleus with that of the egg. In human beings the inheritance of some diseases, so well understood today, was not known at all until the beginning of the twentieth century.

It is however thought that if Mendel’s laws had not been formulated through studies of garden peas, they would have been discovered in the early part of this century through studies of the inheritance of blood groups or of inborn errors of metabolism in man.

Although Mendel published his work in 1865, it was not until 35 years later that its significance was realised when three independent workers published similar results. Due to the vast impact which Mendel’s work had on the discovery of later concepts, the year 1900 is considered to represent the birth year of modern Genetics.

Mendel and the Birth of Mendelism:

One of the peasant families settled in the Czech village of Heinzendorf, then part of Austria, maintained a farm where developing new varieties of apples was their main occupation. In this family was born Gregor Johann Mendel in 1822. Mendel grew up in this farm environment and finished high school at the age of eighteen.

Thereafter he tried to become a tutor at the college in Olmutz but did not succeed. Perhaps due to this failure, or due to lack of money, he returned to his family farm where he spent one year.

After that he did find work as a tutor, but it seems he could not settle down comfortably due to combined pressures of studying, teaching and some financial problems. He therefore left Olmutz (now Brno in Czechoslovakia). He started off as a substitute teacher and in 1848 was ordained as a parish priest.

In 1851 Mendel entered the University of Vienna for training in physics, mathematics and natural sciences. It was at Vienna that Mendel was influenced by two scientists, Franz Unger a plant physiologist, and Christian Doppler, discoverer of the well-known Doppler effect in physics. Perhaps Mendel picked up knowledge here about Kolreuter’s and Gaertner’s hybridisation experiments which formed part of Unger’s teaching courses.

It also seems likely that Mendel sharpened his mathematical awareness through Doppler’s influence on him. After completing his studies at Vienna he returned to Brunn in Moravia, Czechoslovakia in 1854 where he continued to work as priest and as a teacher in high school.