MP Board · Class 12 · Biology · Principles of Inheritance and VariationWhat is chromosomal theory of inheritance? Discuss its key features and explain how it correlates with Mendel's principles of heredity.

Introduction to Chromosomal Theory of Inheritance\nProposed independently by Walter Sutton and Theodore Boveri in 1902, the Chromosomal Theory of Inheritance identifies chromosomes as the carriers of genetic material. They noted that the behavior of chromosomes during meiosis is parallel to the behavior of Mendel's factors (genes). Sutton and Boveri argued that the pairing and separation of a pair of chromosomes would lead to the segregation of a pair of factors they carry, thus providing a physical basis for Mendelian genetics.

Key Features of the Theory

• Parallelism between Genes and Chromosomes: Both genes and chromosomes occur in pairs in diploid somatic cells.
• Behavior during Gamete Formation: Homologous chromosomes separate during anaphase I of meiosis, exactly like the segregation of alleles of a gene during gamete formation.
• Independent Assortment: The distribution of one pair of homologous chromosomes into gametes is independent of any other pair of homologous chromosomes, mirroring Mendel's Law of Independent Assortment.
• Restoration of Diploid Number: Fertilization restores the diploid chromosome number as well as the paired condition of genes in the zygote.

Correlation with Mendel's Principles

1. Law of Segregation Correlation: Mendel stated that allele pairs separate during gamete formation. Sutton and Boveri demonstrated that homologous chromosomes separate during meiosis, thereby carrying the alleles apart.
2. Law of Independent Assortment Correlation: Mendel's second law states that different genes assort independently. Cytological observations proved that non-homologous chromosomes align and segregate independently at the metaphase plate during meiosis I, explaining the molecular and cellular mechanism behind independent assortment.

Experimental Verification\nLater, Thomas Hunt Morgan and his colleagues provided experimental proof for this theory through their work on Drosophila melanogaster (fruit fly), discovering phenomena such as linkage and recombination, which further cemented the chromosomal basis of heredity.