The distinction between point mutations
and chromosomal aberrations
is thus rather superficial. If chromosomes are not studied under the microscope, in certain cases we may not be in a position to say with certainty whether a particular phenotypic character is due to point mutation or due to a structural change. Many mutations, described by de Vries in Oenothera lamarckiana, are
now known to be due to certain numerical and structural changes in chromosomes. These are sometimes described as chromosomal mutations.
For instance, 'gigas'
mutant in O. lamarckiana
was later found to be due to polyploidy. The structural and numerical changes in chromosomes have been discussed in Structural Changes in Chromosomes
and Numerical Changes in Chromosomes
respectively, and this section will be devoted to point (gene) mutations only.