As is well known, Mendel's discoveries lay unrecognized until 1900, when they were independently rediscovered by Correns, De Vries and von Tschermak. Developments after that came quickly, and we do not have time to trace the details, for which I refer you to: "Towards an understanding of the mechanism of heredity" by H L K Whitehouse.
The chromosome theory of Mendelian heredity - that Mendel's factors correspond to locations (loci) along chromosomes - was advanced by Sutton in 1903, with an important extension concerning factor exchanges being added by De Vries; the first observations of non-independent segregation between Mendelian factors (loci) was made by Bateson and colleagues in 1905 and 1906; a basic result on Mendelian frequencies in populations was discovered independently by the mathematician Hardy and the physician Weinberg in 1906; sex-linkage was discovered in the same year by Doncaster and Raynor; and the statisticians Pearson (1904) and Yule (1907) gave mathematical analyses of continuously varying characters from a Mendelian point of view, reaching different conclusions. (References in parentheses can be found in Whitehouse.)
Our interest this week is in non-independent segregation between Mendelian loci, the explanation of this afforded by the theory of crossing-over during meiosis, and in some statistical aspects of this theory. We begin with a clear example of non-independent segregation, also known as linkage between two loci due to Morgan.