An Analysis of Intragenic and Extragenic Mutations of the Plant Color Component of the Rr Gene Complex in Zea mays

Accumulating evidence suggests that extragenic mechanisms play a vital role in the production of seemingly intragenic mutations. Examples of such cases are numerous in the literature. It has been shown that extragenic mutations may be associated not only with gross chromosomal irregularities such as losses, translocations, and inversions but also with minute deficiencies that are invisible cytologically. For example, in the case of pseudoalleles the occurrence of crossing over produces new forms which are not attributed to alterations in the molecular structure of the genetic substance, but result from either minute losses or duplications. Also it has been demonstrated that a change in the action of the gene may be produced by a change in its position.