Salient Features of the Chromosomal Theory of Inheritance

The chromosomal theory rests on four observable features of chromosome behaviour. First, every somatic cell in a multicellular organism traces back to the original zygote through repeated mitotic divisions, so each somatic cell carries two matched sets of chromosomes, one inherited from the mother and one from the father; the corresponding maternal and paternal chromosomes together form a homologous pair. Second, each chromosome keeps a stable, recognisable structure and identity throughout the life of the organism; it does not dissolve into some other chromosome or lose its individuality between one division and the next. Third, every chromosome carries a specific, fixed set of hereditary determiners along its length, which we now call genes. Fourth, and most importantly for connecting cytology to genetics, watching how chromosomes actually move and separate during meiosis gives direct ph …