Polygenic Inheritance and Chromosomal theory of Inheritance

Polygenic Inheritance Definition: Polygenic inheritance is the inheritance of a character controlled by two or more genes (polygenes), where each gene contributes a small additive effect to the phenotype. Characteristics Controlled by multiple genes. Shows continuous variation. Environmental factors often influence expression. No clear-cut phenotypic categories. Examples Human skin color Human height Body weight Wheat kernel color Wheat Kernel Color Example Herman Nilsson-Ehle demonstrated that wheat grain color is controlled by multiple genes. The greater the number of dominant alleles, the darker the grain color. Chromosomal Theory of Inheritance Definition: The chromosomal theory of inheritance states that genes are located on chromosomes, and chromosomes are the carriers of hereditary information from one generation to the next. Proposed By Walter Sutton and Theodor Boveri independently proposed this theory in 1902–1903. Main Postulates 1. Genes are located on chromosomes. 2. Chromosomes occur in pairs in diploid organisms. 3. Homologous chromosomes separate during meiosis. 4. Gametes receive only one chromosome from each pair. 5. Fertilization restores the diploid chromosome number. 6. The behavior of chromosomes during meiosis explains Mendel's laws of inheritance. Significance Provided the physical basis of Mendelian inheritance. Explained segregation and independent assortment. Formed the foundation of modern genetics. Experimental Proof Thomas Hunt Morgan provided strong evidence through experiments on Drosophila melanogaster, demonstrating that genes are located on chromosomes. Difference Between Polygenic Inheritance and Chromosomal Theory Polygenic Inheritance Chromosomal Theory of Inheritance Describes inheritance of traits controlled by many genes. Explains the location and transmission of genes. Produces continuous variation. Explains Mendelian inheritance through chromosome behavior. Concerned with trait expression. Concerned with the mechanism of inheritance. Example: Human skin color. Example: Gene transmission via chromosomes.