Effects of Partial Isolation (Distance), Migration, and Different Fitness Requirements among Environmental Pockets upon Steady State Gene Frequencies

Abstract

Differential fitness requirements within a region can be the dominant force affecting gene frequencies within a population. Formulations for steady frequencies were developed which embraced a 2-dimentional migration pattern. A simple distance transformation removed migration and isolation parameters from the formulations yielding a useful inequality, P>l-(d-/dcOw)2 Critical distance (dc) can be bracketed from theoretical considerations and the probability of emigrating (1-P), the migration unit (Ow), and the distance (d) are experimental measures. A clinal variation in fitness led to a narrow hybrid belt. Peripheral: areas of differential fitness can lead to an extended hybrid belt. Migration can mask a pocket of differential fitness. Critical pocket sizes corresponding to selected conditions were given. The race structure for cultivated maize in Mexico was interpreted as a product of a migrating population where colonies were individual farmer collections. Of particular interest was whether selection for ear characteristics by the lay farmer could yield a collection which was dissimilar morphologically from its neighbors. Solutions suggested that isolation among cultivated fields (collections) was not sufficiently complete for this divergence to occur.