Allen notes on principles of inheritance and variation
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Principles of Inheritance and Variation – CBSE Notes for Class 12 Biology
June 3, 2019 by Sastry CBSE
Principles of Inheritance and Variation – CBSE Notes for Class 12 Biology
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Mendel’s Laws of Inheritance:
1. Genetics is the branch of biology, which deals with inheritance and variation of characters from parents to offspring.
2. Inheritance is the process by which characters or traits are transferred from one generation to the next.
3. Variation is the degree by which progeny differs from each other and with their parents. Humans knew from as early as 8000-1000 BC, that one of the causes of variation was hidden in sexual reproduction.
4. Gregor Johann Mendel, for the first time conducted experiments to understand the pattern of inheritance of variation in living beings.
5. Mendel’s Experimental Material
(i) He conducted experiments on garden pea plant (Pisum sativum) for seven years (1856-1863) and proposed the laws of inheritance in living organisms.
(ii) He selected garden pea plant as a sample for experiment because of:
(a) Easy availability on a large scale.
(b) Many varieties are available with distinct characteristics.
(c) They are self-pollinated and can be cross-pollinated easily in case self-pollination does not occur.
(iii) Mendel selected 14 true-breeding (a breeding line which has undergone continuous self-pollination shows stable trait inheritance and expression for several generations) pea plant varieties, as pairs, which were similar except for one character with contrasting traits.
Seven contrasting characters and their traits as taken by Mendel