English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

A N I M A L and plant breeders often face the problem of selection for several characters simultaneously, but laboratory experiments on selection deal usually with a single trait at a time. Even so, comparison of the original strain with that resulting from selection sometimes discloses differences in traits additional to that for which the selection was made. There are several causes which can bring about such correlated responses to selection. One of them is pleiotropismthe genes affecting the trait for which one selects may have manifold effects. Another is linkage-the gene selected may be associated in the chromosomes of a given strain with genes for quite other characteristics. Still another is that an artificial selection for a certain trait may cause a lowering of the fitness, which may then be compensated by natural selection for alleles at other loci. In natural populations, natural selection is likely to occur for several or many qualities at a time, the combination of which results in a satisfactory adaptedness to changing environmental conditions. This was most likely the case in human populations, during the transitions from their pristine state to culture, to civilization, to technologically developed societies. An experimental essay, the results of which are reported in the present article, was contrived as a model of such multiple selection in the fly, Drosophila pseudoobscura. The geotaxis classification mazes, modeled after HIRSCH (1962) and HIRSCH and ERLENMEYER-KIMLING ( 1962), permit screening without undue amount of labor of fairly large numbers of flies in each generation (300 females and 300 males. i.e., a total of 600). The individuals which have made mostly downward, or mostly upward choices in the maze are Selected as parents of the succeeding generations. Such selection produces genetically positively or negatively geotactic flies, as shown in Drosophila melanogaster by the authors referred to above, and by DOBZHANSKY and SPASSKY (1962,1967) in D. pseudoobscura. WADDINGTON (1959, 1960) selected D. melanogaster for the ability of the larvae to survive feeding on a medium containing as much as 7% sodium chloride. Although D. pseudoobscura proved to be less pliant genetically in this respect, we did increase the salt tolerance significantly in the experiments to be reported. It is well known that the variations in the gene arrangement in the third chromosomes of D. pseudoobscura are maintained in natural as well as in experimental

AN EXPERIMENT ON MIGRATION AND SIMULTANEOUS SELECTION FOR SEVERAL TRAITS IN DROSOPHILA PSEUDOOBSCURA