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COURSE Principles of inheritance and variations Lesson 15 Cromosomal theory of inheritance Dr. Praveen Kumar Agrawal M.Sc., Ph.D., CSIR NET (JRF). SRF, GATE 21Years of Pre-medical teaching experience
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CHROMOSOMAL THEORY OF INHERITANCE On the basis of Mendel's work, we can understand the inheritance patterns, at the level of genes (factors). Before the publication of Mendel's work, a little was known about the location and function of chromosomes. The role of the chromosomes and their relation with Mendelian factors (genes) was worked out only after the publication of Mendel's work. The discovery of meiotic cell division helped very much in understanding the nature and behaviour of chromosomes. In 1902, Sutton and Boveri noted the role of chromosomes. They found that the behaviour of chromosomes was parallel to the behaviour of genes. Parallelism between Genes (Mendelian Factors) and Chromosomes Both chromosomes and the genes are found in pairs. During gametogenesis homologous chromosomes get separated, similarly genes (alleles) also get separated during gametogenesis (meiosis) The paired condition of both chromosomes and genes is restored after fertilisation. These observations led to the postulation of the 'Chromosomal theory of inheritance'.
Chromosomal Theory of Inheritance The chromosomal theory of inheritance was proposed by W. Sutton and T. Boveri (independently) in 1902. The theory states that chromosomes bear Mendelian factors (or genes). Chromosomes are the vehicles of heredity information. It is the chromosome that segregate during gametogenesis and assort independently. (Since genes are located on chromosomes, they also get segregated and assort independently) Important features of the theory are: Zygote is the diploid cell, formed by fertilisation. During fertilization, zygote receives one maternal set of chromosomes (from ovum) and one paternal set of chromosomes (from father). The two chromosomes of one type (from each set) together form a homologous pair. uniqueness. the characters of the organisms Throughout the life of the individual, chromosomes retain their individuality and structural e Each chromosome carries genes (Mendelian factors) which play important role in determining During meiosis (gamete formation) the two chromosomes of a homologous pair get separated from each other. Since factors (genes) are located on chromosomes, they also get separated. This theory was further expanded by T. H. Morgan, Alfred H. Sturtevant and Calvin B. Bridges. The term factor' (used by Mendel) was replaced with the term 'Gene' by Johannsen in 1909 Thomas Hunt Morgan carried out his experiments of fruit fly (Drosophila melanogaster) and provided experimental proof in favour of 'Chromosomal theory of inheritance'. He also discovered the basis of varions, produced by sexual reproduction
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