Genetics : Pleiotropy
It is an established fact that a specific gene controls a specific phenotypic trait. This finding is not always true. Studies on 'gene expression' have revealed that a gene often influences more than one phenotypic trait. This phenomenon of multiple effects of a single gene is called pleiotropism. In such a genic influence more conspicuous expression of a phenotypic trait by a gene is called its major effect. If the gene causes other less conspicuous phenotypic changes, it is known as secondary effect. Such genes responsible for multiple effects are called pleiotropic genes.
Vestigeal wings in Drosophila are caused by a recessive gene in homozygous condition. A keen observation has shown that this gene affects other traits as well. They are
(i) the small halters or balancers behind the wing
(ii) structure of reproductive organs
(iii) egg production
(iv) life duration and
(v) bristles on the body.
Genetics is the study of inheritance or heredity. It deals with the trans-mission of characters, specific for that particular type of plant or animal, from the parent to the offspring of the next generation.
The history of Genetics is closely linked with the ancient cultural his-tory of man. It began ten thousand years ago, when human beings changed from a nomadic life to the life of settlers. As settlers in early civilization they started living as groups. A need for food forced them to explore nature and adopt agriculture. The agricultural revolution in early human civilization opened the doors for very rapid improvements in human culture. They learnt to iden-tify plants that could be grown and cultivated. Several cultivation processes evolved. They started selecting suitable varieties for agriculture.
Simultaneously they started domestication of animals. Many animals were brought under human control. Gradually they understood their reproduc-tive methods. Hybridisation and generation of new varieties of animals like horses, dogs, cats and cattle happened. The idea of Genetics was adopted in everyday practice.
A scientific approach to understand inheritance was initially made by Gregor Mendel. He did hybridization experiments in Pisum sativum more out of curiosity and his devotion to science. He applied statistical methods to biological research.
Since the 'rediscovery' of Mendelism in 1900, Genetics has made rapid developments. The advancement in cell biology, microscopy, biochemistry and other disciplines provided the necessary infrastructure for this science to reach its climax. As of to-day all processes and causes for inheritance are well understood. Through the developments in Genetic Engineering, Biotechnol-ogy, Tissue culture and other methods we are trying to exploit nature. How-ever, the steady processes of dominance of human beings on earth through their knowledge of science and skill in technology will also ensure the safety of earth in the times to come. In such a safeguarding the science of Genetics with all its related fields will play a key role.