Cell Organelles and Their Functions

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Introduction
Genetics: the science, which deals with the principles of heredity and variation. Heredity: transmission of characters from parents to their off spring. Variation: Differences for various characters among the individuals of the same species. Types of variation: 1. Environmental and 2. Hereditary

1. Heredity variation: Variation observed among the individuals of the same species due to difference in their genetic constitution is termed as heredity variation. 2. Environmental variation: Two individuals with the same genotype may become different in phenotype when they come into contact with different conditions of food, temp., light, humidity and other external factors. Such differences among organisms of same heredity are called as an environmental variation. Environment: can be defined as sum total of an external conditions which influence on organism. Plant genetics: A branch of genetics, which deals with inheritance and variation of characters in plant species. Cytology: cytology may be defined as that branch of science, which deals with the morphology and physiology of the cell. Cytogenetics: Combined study of cytology and genetics.

History Events (cytology and Genetics)

|Year |Events | |1665 |R. Hooke – Introduced the term “cell” | |1830 |J. E. Purkinje– Introduced the term “protoplasm” | |1833 |Brown discovered the cell nucleus in flowering plant Tredescantia | |1834 |Von Mohl described cell division and emphasized the importance of protoplasm | |1838 |M. J. Schleiden – cell concept in plants | |1839 |T. Schwann applied the cell concept to animals | |1846 |K. Nageli showed that plant cells arise from the division of pre-existing cells | |1855 |R. Virchow – confirmed the principle that cell arise only from pre-existing cells. (Omnis cellula e cellula) | |1865 |G. Mendel (1822-1884) developed the fundamental principles of heredity. | | |“Father of Genetics” | |1882 |W. Fleming – proposed the term meiosis | |1888 |W. Waldeyer – introduced the term chromosome | | |Strasburger showed that the chromosome number is halved in the cell when gametes are formed | |1892 |A. Weismann – Germplasm theory | |1900 |Karl Correns, Hugo de Vries and E. Tschermak rediscovered the fundamental principles of heredity | |1902 |Mc - Clung identified the sex – chromosome in Hemiptera | | |W. S. Sutton showed significance of reduction division; proposed the chromosome theory of heredity | |1905 |Farmer coined the term meiosis with J. E. Moore | |1906 |Bateson coined the term “Genetics”...
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