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4 Mumbai Synopsis Subject – Biology Standard – Xii 1 ATOMIC ENERGY CENTRAL SCHOOL- 4 MUMBAI SYNOPSIS SUBJECT – BIOLOGY STANDARD – XII UNIT – VII GENETICS AND EVOLUTION CHAPTER – 5 PRINCIPLES OF INHERITANCE AND VARIATION MODULE – 1/16 Prepared By: Sanghmitra P Pratape 2 Ch – 5 Principles of Inheritance and variation Module 1/16 Topics to be covered: - Definitions – Genetics, Inheritance, variation - The Father of Genetics – A glimpse to Mendel’s Life - Mendel’s experiments on Pea plant - Laws of Inheritance Genetics – A branch of biology that deals with inheritance, as well as the variation of characters from parents to offsprings. The term was coined by Bateson in 1906. Inheritance – It is the process by which characters are passed from parents to offsprings; it is the basis of heredity. Variation – It is the degree by which progeny differ from their parents. Father of Genetics –Gregor Johann Mendel (1822 – 1884): Mendel was born in Silisian, a village in Austria, on July 22, 1822 to a farmer’s family. He was a brilliant student and studied philosophy for several years. After schooling, Mendel joined an Augustinian monastery of St Thomas at Brunn in 1843 at the age of 21 yrs. In 1851, Mendel was sent to University of Vienna for study of Botany and Physics. He was the first to demonstrate the mechanism of transmission of characters from one generation to the other. He also gave laws of inheritance. They constitute the foundations of genetics. Mendel’s Laws of Inheritance: Mendel conducted hybridization experiments on garden peas for seven years from 1856 – 1863 and proposed the laws of 3 inheritance in living organisms. During his investigations into inheritance patterns for the first time statistical analysis and mathematical logic were applied to problems in biology. He confirmed the purity of his experimental materials through inbreeding. Initially he took 34 pairs of varieties of Pea plants then 22 but finally he worked with 7 pairs of varieties. The plants differed from each other in characters such as: plant height, flower color, flower position, pod shape, pod color, seed color, and seed shape. All the selected varieties were pure lines or true breeding. A true breeding line is one that, having undergone continuous self pollination, shows the stable trait inheritance and expression for several generations. Mendel conducted cross pollination or artificial pollination in his experiments using several true breeding varieties. (Artificial pollination is done by Emasculating one flower, which can be used as female flower.)But his work remained unnoticed and unappreciated for some 34 years. It was in 1900 that three workers independently rediscovered the principles of heredity already worked out by Mendel. They were Hugo de Vries of Holland, Carl Correns from Germany and Erich von Tschermak of Austria. Reasons for Mendel’s success: 1. He selected only pure breeding varieties of Pea plant for his experiments. 2. He selected contrasting traits like tall and dwarf. 3. He took only one trait at a time for his experiments. 4. He studied one trait for 2 or more generations. 5. He performed reciprocal crosses and raised large progenies. 6. Pea plant that he selected for his experiments is naturally a self breeding plant but can be cross bred manually. 7. This plant can be grown on small plot or even in a pot. 8. He was lucky enough to not to get linked genes. 4 ACKNOWLEDGEMENT The following text books were referred to complete the synopsis: 1. Text book of NCERT Class – XII 2. Trueman’s Elementary Biology Part – 2 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx .
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