Rigid vs. Flexible Chromosomal Polymorphisms in Drosophila

Abstract

Balanced chromo-somal polymorphism occurs in populations of many species of Drosophila. This polymorphism may be extremely sensitive to variations in the environment; populations then respond by genetic changes to differences in the climatic, elevational, and biotic conditions of the localities which they inhabit, and even to the succession of the seasons of the year. Other equally polymorphic populations of the same or of different species appear, however, to be stabilized in their genetic composition and unresponsive to environmental variations. Examples of such apparent insensitivity are given. The origins of these different forms of behavior are discussed.