The question about heredity intrigued many scientists. Gregor Johann Mendel (1822 -1884), an Austrian monk undertook the laborious task of finding the answers. He selected some pea plants, grew them year after year, compiled a lot of data, analysed and postulated certain laws of inheritance for the first time.
His remarkable work, however, got recognized years after his death when Correns, Tschermak and Hugo de Vries came to the same conclusions as Mendel did, after independently carrying out experiments in their own countries.
Mendel’s laws state that:
Every feature or character (for example colour of flowers, height of plant, colour and texture of seed, colour and texture of pods and location of flower on the plant) is controlled by a pair of factors. During the formation of gametes, one factor goes to one gamete and its pair to another gamete. Thus the two factors of a pair segregate or separate during gamete formation. Upon fertilization, the combination of factors expresses the feature. (1st law).
Out of the two factors controlling a certain feature, the dominant one may express inspite of the presence of the other. The other factor expresses only in the absence of the dominant factor and is termed recessive (2nd law).
For example, factor for tallness in the pea plant always expresses in the offspring but dwarfness expresses only if factor for tallness is not present.
Mendel also postulated two other laws called "law of parental equivalence" and, "law of independent assortment".
The first law defined is universal. Scientists later observed deviations from the other Mendelian laws. Sutton in 1902, working with grasshopper chromosomes confirmed that Mendelian factors were present in chromosomes. Still later the term gene replaced the term factor. In other words, genes are present on chromosomes.