The Austria monk Gregor Johann Mendel was first to explain the mechanism involved in transmission of characters from one parent to the offspring�s generation after generation. He is considered as the pioneer of modern genetics and is called �Father of Genetics�.
He started his historic experiments with garden pea (Pisum sativum) in the monastery garden. The experimentation work continued for about nine years from 1856 to 1864. The results of these classical experiments and Mendel�s conclusion were published in an obscure journal- The Annual Proceedings of the National History Society of Brunn in 1865.
Mendel postulated three laws:
Law of Dominance and recessiveness -When two homozygous individuals with one or more sets of contrasting characters are crossed the characters that appear in the F1 hybrids are dominant characters and those do not appear in F1 are recessive characters.
Critical appreciation of Law of Dominance: Scientist conducted crossbreeding experiments to find out the applicability of law of dominance. The experiments were conducted by Correns on peas and maize, by Tschemark on peas, by Deveris on maize etc. and by Bateson and his collaborators on a variety of organisms, by Davenport on poultry and many others. These scientist observed that a large number of characters in various organisms are related as dominant and recessive.
Importance of Law of Dominance: The phenomenon of dominance is of practical importance as the normal dominant characters in the hybrids mask the harmful recessive characters. In human beings a form of idiocy, diabetes, hemophilia etc is recessive characters. A person hybrid for any of these recessive characteristics appears perfectly normal. Thus harmful recessive genes can exist foe several generations without expressing themselves.
Law of Segregation (Law of purity of Gametes)- according to this law when a pair of contrasting factors or genes or allelomorphs are brought together in a heterozygote the two number of allelic pair remain together without being contaminated and gametes are formed from the hybrid, the two separate out from each other and only one enter each gamete.
Critical appreciation of Law of Segregation: It has been confirmed by cytological studies that dominance or no dominance, the law of segregation holds good to all cases. Its far reaching applicability has made it a rare biological generalization.
Law of Independent Assortment- If the inheritance of more than one pair of characters (two pairs or more) is studied simultaneously, the factor or genes or each pair of chromosome/ characters assort out independently of the other pairs.
Critical appreciation of Law of Independent Assortment: The law of independent assortment fails to have a universal applicability. Cytological studies have revealed that only those allelomorphs assort independently during meiosis, which are located at different homologous pairs of chromosomes. But, if the allelomorphs for different characters are present in the same homologous pair of chromosomes, these are passed to the same gamete. Law of independent assortment does not apply to such cases.
Biological Significance of Mendel�s Work:
Mendel�s work remained buried for about three decades, but after its rediscovery, the laws are being used for the various branches of breeding. These are use for improving the varieties of fowls and their eggs; in obtaining rust-resistant and disease resistant varieties of grains. Various new breeds of horses and dogs are obtained by cross breeding experiments. The science of Eugenics is the outcome of Mendelism, which deals with the betterment of human race.
