Formulation of chromosome theory

Content
Physical Basis of Heredity 4. The Chromosome Theory of Inheritance
Association of paternal and maternal chromosomes at meiosis
Qualitative differences between chromosomes
Formulation of chromosome theory
Sex chromosomes and chromosome theory
On the basis of findings of Montgomery and Boveri and on the basis of his own studies, W.S. Sutton for the first time in 1903 formulated chromosome theory of Mendelian inheritance in clear terms. He drew attention to following features which suggested that Mendelian factors should be located on chromosomes :

(i) There is a resemblance between separation of homologous chromosomes during anaphase I of meiosis and the postulated separation of character differences at the time of gamete formation.

(ii) If each pair of homologous chromosomes is so oriented at metaphase I, so that in a pair the orientation of maternal and paternal chromosomes, towards specific poles is independent of the orientation of these chromosomes in the other pair, we expect that 2n combinations are possible (n = haploid chromosome number). This is true of Mendelian factors also. This will further suggest that in sea urchin with n = 18, n18 = 262,144 possible combinations of maternal and paternal chromosomes will be available. Therefore, there is parallelism between presumed independent assortment of homologous chromosomes at meiosis and Mendel's principle of independent assortment. Confirmation of random orientation of different chromosome pairs came by the use of sex chromosomes, which will receive a detailed treatment in Molecular Mechanisms of Recombination.